Background: The reproductive histology in the decapods have been widely documented; however, this information has never been reported in Emerita taiwanesis, one of profitable species for aquaculture business in Southeast Asia. Material and Methods: The gametogenic maturation and embryonic development of sand crabs E. taiwanesis with carapace widths of 4-5 cm (n = 20 for each sex) from Sangchan Beach, Thailand were examined by histological techniques and light microscopy. Results: The gonadal structure was located underneath the carapace at dorsal area of the body. Under histological techniques, the ovarian maturation was observed to be enclosed with a thin layer of ovarian wall. The different phases of developing oocytes could be classified into five stages: 1) Oc1 (previtellogenic stage), 2) Oc2 (early vitellogenic stages), 3) Oc3 (late vitellogenic stage), Oc4 (mature oocyte) and Oc5 (atretic oocyte). The spermatogenic maturation occurred at the same time as female ovarian maturation. The spermatogenic stage was clearly divided into five stages: spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa. Additionally, different timing of its embryonic development was observed, and the embryos could be categorized into three major stages: 1) early development (cleavage, blastula, and gastrula), 2) early organogenesis (post-gastrula) and 3) late organogenesis. Conclusion: In this study, histological observation of oogenesis and spermatogenesis as well as embryogenesis of sand crab E. taiwanesis highlights the conserved pattern of gametogenic maturation among decapod, which can lead to understanding of the reproductive cycle, physiology, and aquaculture strategies of this economically important crustacean in the Gulf of Thailand. [ABSTRACT FROM AUTHOR]