Abstract Mating behaviors and mating systems in decapod crustaceans have attracted significant attentions. Dendrobranchiata and several infraorders of Pleocyemata (Caridea, Achelata, Astacidea, Anomura, and Brachyura) are the focal taxa. Virtually nothing is known about the members of Thalassinidea (recently separated into Axiidea including Callianassidae and Gebiidea including Upogebiidae) due to observational difficulties for their deep burrow-dwelling habit. Giving a little sediment and minute artificial tubes for one male and two females of the callianassid, Nihonotrypaea harmandi, in small transparent containers under illumination, observations and video-recordings of mating behaviors were made for the one pair three times, for the first time for Axiidea. The combined time schedule for each behavioral component was obtained. In inactive states, the shrimps stayed in their own burrows. The pre-mating visit was initiated by the male 3–4 d before the copulation, in which mutual signaling between sexes with movement of antennules, maxillipeds, chelipeds, and pleopods occurred. The final access was made by the hard-shelled female. The copulation lasted 91–105 s, with male onto female, during which a single spermatophore was transferred to sternite 8 surface with no sperm-storage structure. After the copulation, intimate exchanges occurred for 3–14 min. The female then isolated herself to an enclosed space for 60–74 min, during which oviposition started 44 min after the copulation, with embryo attachment to pleopods 1–2 completed in 12 min. The embryos were carried for 13–19 d before hatching. These findings would become basic to the understanding of thalassinidean shrimp population dynamics conducive to their key roles as benthic community organizers and ecosystem engineers in marine soft sediments.