Knowledge on morphology and size of otoliths and their correlation with fish sizes are essential in fish development determination. Yet, little is known about gobies in the Mekong Delta of Vietnam (VMD), including Glossogobius aureus, a commercial fish. This study was conducted from January 2020 to December 2020, in order to understand the morphology and size of otolith and their relationship with fish size, based on a cohort of 742 individuals. Fish was monthly caught by trawl nets in four sites, including Cai Rang - Can Tho (CRCT), Long Phu - Soc Trang (LPST), Hoa Binh - Bac Lieu (HBBL) and Dam Doi - Ca Mau (DDCM). The four sampling sites had apparent differences in environmental conditions, especially in salinity. Data analysis showed that otoliths’ shapes were elliptic and the otolith surface on the side of the fish skull had is rough with deep depressions, whereas the reverse side had a smooth surface, without indentations. The top edge was irregular wavy lines, while the bottom edge was relatively flat. There was no difference in the size of the left and right otoliths, and the weight of otoliths varied with the season and site, but it does not change with the gender. The weight of the otolith was observed relationship with the total length (TL), weight (W), body height (BD) and head length (HL) at all study sites (r2>0.61 for all cases). It indicated that the otolith weight could be considered as a criterion used to determine the size of fish.