The upper parts are pinkish buff, sandy brown, or grayish brown, and the underparts, hands, and feet are white. The tail, dark above and white below, is thickly haired, tufted, and longer than the head and body. The large ears are conspicuous. There are no cheek pouches. One feature distinguishing Calomyscus from Peromyscus is the number of roots the molar teeth have.
Females have six mammae.
Calomyscus is active only at night during the summer, but it is also active by day in the autumn and winter. It feeds mainly on seeds, also consumes flowers and leaves, and readily eats animal matter. There apparently is a lengthy breeding season, and some females have two litters per year. Adult coloration and size are attained in 6-8 months. The Soviet Union now classifies C. urartensis as rare and C. mystax as indeterminate.