The mating behavior and fertilization capacity of three different ontogenetic stages of male rock shrimp Rhynchocinetes typus were examined. The first ontogenetic stage is the typus morphotype, which is similar in morphology to the female. The last ontogenetic stage, the robustus morphotype, is characterized by extremely long third maxillipeds and powerful chelae. During ontogenetic development between these two morphs, males undergo several intermediate molts, which are termed “intermedius.” In mating experiments with pairs of single males and females, all ontogenetic male stages (typus, intermedius, robustus) behaved in a similar manner. First, they followed the female, then embraced it with the second pereiopods and held it beneath their bodies, encaged by the pereiopods, the 3^rd maxillipeds, and the abdomen. Various stimulating and checking behaviors preceded the placement of the first spermatophore, which usually coincided with the start of the spawning process. Most spermatophores were placed during the first 30 minutes of spawning. Following spermatophore placement, males guarded the females during almost the entire spawning process, which could last longer than 120 minutes. The number of spermatophore transfer events during the mating process varied significantly between the two extreme ontogenetic male stages, being typus greater than robustus. No significant differences were found in the percentage of eggs lost by females that were fertilized by the three ontogenetic male stages. These results suggest that all male stages have the same potential to mate successfully with females in a competition-free environment. However, we propose that male mating success may change drastically when different ontogenetic male stages compete directly for access to reproductive females.