Ninken (忍犬, English TV: Ninja Hounds, Literally meaning: Ninja Dogs) are essentially dogs that have heightened senses and abilities and as such are able to work with ninja. Although the dogs belonging to the members of the Inuzuka clan are ninken, the phrase is usually used in reference to the pack of eight ninken summoned by Kakashi Hatake. Kakashi's ninken have shown the ability to use human language, capacity of developing combat strategies and investigative sense as well.

Kakashi can also summon them for special purposes, like he does with his Summoning: Earth Release: Tracking Fang Technique. With this technique, the dogs can travel through the ground following the scent of their target, emerging when the target is found and holding them in place. They all have a face-shaped design on their backs called Henohenomoheji (へのへのもへじ) — which is the sound made when all the characters in the face are put together. Appropriately enough, children use this design as the face for their scarecrows, which is "kakashi" in Japanese.

Known Ninken

Kakashi's Ninken

Inuzuka Clan's Ninken