Relative growth of cheliped and abdomen was studied in the thalassinidean shrimp Laomedia astacina de Haan, 1841 based on samples taken from the Seto Inland Sea, Japan. A total of 108 individuals was collected and analysed. The sex ratio did not differ from 1:1 and sexual size dimorphism was not evident. Laomedia astacina was heterochelous, with the major claw slightly larger and stouter than the minor claw. The proportions of right and left major claws did not differ significantly from 1:1 and did not change with shrimp size. Both sexes exhibited a positive allometry in both cheliped types. Sexual dimorphism was observed in the width of the abdomen, but not observed in the chelipeds.