They are classified as a Working Dog. The English Bulldog from which the Bullmastiff is bred from is quite different from today's modern version. The English Bulldog of the 19th century was a more athletic dog than many of today's, although the loyal and calm temperments are still the same. Description AKC Standards removed due to copyright violation concerns.
They have been described as: intelligent, loyal, stubborn, laid back, family oriented, stoic, and even-tempered. Bullmastiffs rarely bark unless there is a reason. There is a minimal amount of slobbering associated with a Bullmastiff, usually after eating or drinking. They are a dog that requires consistent and fair training. They do not take well to being bullied into something but will accept leadership. Obedience work with Bullmastiffs can be challenging as they are independent thinkers, but once learned it sticks!
The Bullmastiff seems to be very easy-going and as such tends to integrate well with other dogs. But as with any breed, you should start socialization early. Puppy kindergarten type situations are definitely recommended. As far as the Bullmastiff's relationship to other animals (other than dogs) I can only draw on my own experience; my Bullmastiff is extremely gentle with cats, birds, hamsters, etc. (can anyone else give me any info?). I have heard from others that size rather than aggressiveness is often more an issue when being around other animals. Often Bullmastiffs don't realize their size and can hurt a smaller dog, or cat, with rough-house play.
One note of caution, e-mailed to me by a long time breeder of Bullmastiffs, is that, being a territorial breed, sexually in tact males and females put together, may lead to problems. Caution should be used when introducing studs and bitches to one another - unless you know they are extremely passive.
In relationship to people, Bullmastiffs tend to be one family dogs. They bond extremely close with "their" people and can be suspicious of strangers. Early puppy interaction with lots of different people is key to overcoming potential problems due to this trait. This being said, if the family is loving and welcoming, getting a grown Bullmastiff dog through rescue contacts is a wonderful option, for those that don't want to go through the early "puppy" years. This is a quote from a long-time breeder of Bullmastiffs and rescue contact, "An overwhelming percentage of rescue dogs (dogs who have the most reason to be wary) settle in new homes with the greatest of ease. Almost all of the Bullmastiffs I meet in other people's homes are immediately outgoing and interested in being my best friend. Believe it or not Bullmastiffs can be quite cuddly and demonstrative. They must be integrated as a member of the family. I would say they are not very suitable for being an outdoor dog.
Bullmastiffs are also very good with children. Their easy going nature and calmness, tend to make them able to tolerate the energy of younger kids. But again, due to their size constant parental supervision is required.
They are a naturally protective dog. They have a suspicious nature in regards to strangers and "size" people up. Sufficient socialization is extremely important due to this fact. They also naturally "guard" their family members. Bullmastiffs are constantly attentive and curious about their surroundings and will be alarmed if any danger is perceived to their pack. These two factors make, in my opinion, make on-going training and early puppy socialization, all important. Without it, Bullmastiffs can become over-protective and over-aggressive towards strangers and other dogs, etc. The most amazing thing about Bullmastiffs is their ability to sense people's intentions - they seem to know instinctively the difference between a "bad" person and a harmless visitor to their property.
Bullmastiffs do not tend to tolerate LARGE variances in temperature. They do not like extreme heat or extreme cold. I have heard from people that some Bullmastiffs do like the snow.
NOTE: Bullmastiffs do tend to have a high tolerance for pain and often will not complain about discomfort until the condition is quite bad.
Please note that puppies of any breed are a LOT of work and require without a doubt, time, energy and love. On average a puppy requires at least 4 hours per day and probably more if you are into any type of training.
Ear cleaning is a must as is nail clipping.
Would recommend teeth cleaning using an enzymatic toothpaste.