Like almost all dogs, Jack Russells are not dangerous at all if they are well treated and properly trained. Being quite small, they aren't the kind of dogs you would normally think of as dangerous anyway, but there have been some cases of Jack Russells attacking people, which has led to some discussion of this subject.

Like all terriers, they are very active, bright and curious; they are also typical terriers in that they are bossy, and you have to show them straight away who is in charge. If they are given clear discipline, plenty of exercise and love, Jack Russells make lovely pets (though they aren't the best animals to have around small children); but in the wrong hands they can turn out badly. They are really working dogs, and not lapdogs that are happy to sit around all day. They also like to fight; usually against other dogs, but if not kept under control some of them will bite a human. However, as with most cases of animals behaving badly, it is nearly always the owner that is the problem and not the dog.