Japanese spaniel, breed of dainty, alert toy dog probably originating in ancient China and developed in Japan over many centuries. It stands about 9 in. (22.9 cm) high at the shoulder and weighs about 7 lb (3.2 kg). Its long, profuse coat is straight and silky and is usually black and white or any of various shades of red and white. Traditionally given as the gift of emperors, the Japanese spaniel was introduced into the West by Commodore Matthew Perry in the mid-19th cent. Today it is a popular house pet. See dog.