A study on biometrical analysis was carried out to check the applicability of Dyar’s principle to the larval stages of Earias vittella (Fabricius), when the larvae were reared on okra fruits in room temperature (260 to 300C). The measurement of head capsule width of the larvae was fell into four well defined groups as an instar. The mean value of the observed head capsule (0.32 to 1.37 mm) and calculated head width (0.31 to 1.38 mm) and progression factors (1.03 to 1.65) were closed to each other, which indicated that the width of head capsule of E. vittella was more or less constant for a particular instar. The observed and estimated progression factors were approximately close to each other indicating the increase in head width that follows Dyar’s Law. The progression factors determined from body length and width indicated that the great deviation to provide any support for the theory suggested by Przibran and Megusar (1912). The value of R2 among the variables viz., head capsule width, larval body length and larval body width was 0.999. This indicated a very high predictability of head capsule width through larval body length and larval body width.