Standard males between 65 and 75 cm high at the withers and weigh at least 50 kg, and up to 85kg. Females are 60 to 70 cm, high at the withers and weigh at least 40 kg.

They were taught to chase down jaguars, cattle, and other animals, as well as runaway slaves. The dogs would grab the slave or animals by the neck and hold them until the farmer arrived. This instinct can be observed among puppies when they are playing.

The Brazilian Mastiffs are known to be naturally protective. It is also known for its extreme wariness of strangers and agility when protecting or defending its master. Despite extensive socialization, the fila is instinctively protective and will naturally guard and protect its owner, their family members and the family pets; this is not something that needs to be trained, it is an innate trait.