We investigated the effects of delayed mating on the reproductive success of female spiny king crabs, Paralithodes brevipes, in laboratory experiments where the duration between female molting and mating was controlled. Females mated and spawned irrespective of the number of days after their molting within 20 days. However, as the number of days after female molting increased, the fertilization rate decreased significantly. Females that spawned at 16 or more days after molting lost significantly more eggs than females that spawned at ≤12 days after molting. The percentage of detached eggs that developed normally to the morula stage decreased significantly in females mated at 20 days after their molting. The percentage of females with a few or no eggs tended to increase as time elapsed between molting and mating increased. Thus, the increased number of days after female molting influenced the reproductive success of spiny king crab females, and females had an optimal duration to mate after their molt. Our results suggest that the present fisheries of this species, in which only larger males are harvested, may affect female reproductive success by decreasing the availability of male mates. An adequate management of this species needs to include these considerations.