Larval morphological characters such as body color and stripe pattern were analyzed to get morphological genetic markers of beet armyworm, Spodoptera exigua (Hiibner). Body color was varied from light green to dark brown with diets. Stripe characters were classified by the presence of dorsal and lateral lines: three stripes with both lines, one stripe with dorsal line only, and zero stripe. Proportions of each stripe character increased with successive selections for its own character. Three stripe was dominant to one stripe when they were crossed. The estimated heritability in narrow sense (h2) of the stripe pattern was 0.50k0.42. About two fold more females than males were produced in zero stripe line. Stripe pattern was not significantly changed by different diets except in welsh onion which had lower proportion of three stripe individuals than that of the expected. Larval stripe pattern was also correlated with larval and pupal developmental rates and cold hardiness but not with insecticide susceptibility.