Sure! It is a healthy sort of fruit and most dogs love bananas! They contain lots of fibre, energy and vitamins, amongst others potassium. This mineral is important in many processes, such as lowering blood pressure, maintaining fluid balance, muscle contraction and nerve conduction. There are also several B vitamins in it.
Providing a piece on a regular basis is an excellent addition to their daily menu for variation. Of course, you give a small dog a piece, a (medium to) large dog can easily eat an entire one. Preferably give a ripe banana because of the better digestibility. Bananas contain a lot of energy compared to other fruits. For dogs that too fat or have a low energy level, a small piece is more than enough.