The protective helmet includes a hard plastic shell member which is configured to fit over the top of the horse's head, with openings for the ears of the horse. The shell member has a particular configuration, with a front edge which fits around the top of the eyes of the horse and curves slightly downwardly between the eyes, side edges which extend from the front edge to the rear of the horse's head, and a rear edge which is located a distance down the back of the neck of the horse. An interior member is positioned on the interior surface of the shell member, made of soft, pliable material which conforms to the surface configuration of the horse's head when the helmet is secured thereto. A strap assembly extends between the respective sides edges of the shell member, including a buckle or other attachment portion which permits adjustable securement of the helmet on the horse's head.