Trypauchen vagina (Bloch & Schneider, 1801) is one of two gobiid fishes of the genus Trypauchen (Gobiidae), and a potential commercial fish in Mekong Delta, Vietnam. A study on the goby T. vagina was investigated in Cu Lao Dung district, Soc Trang province, Mekong Delta, Vietnam, to establish some basic population biology parameters. A total of 179 individuals were caught in Kinh Ba river in this area by gill net to determine the length-length and length-weight relationships of this species. After determining sex by external features, total length (TL in cm), standard length (SL in cm) and body weight (W in g) of this goby were measured, respectively. This study ran for six months, from January 2013 to June 2013. The mean lengths and average body weights for total fish, female, male and unsexed individuals were significantly different at confident level 95%, except male and female. The length-weight relationships of total fish, female, male and unsexed were highly correlated with high regression coefficient which were 0.974, 0.931, 0.954 and 0.635, correspondingly (Fig. 1). These values were not notably different between total fish, male and female groups, whereas they were considerably higher than that of unsexed group at meaningful level ? = 0.05. The proportion of male and female groups were not substantially different at confident level 95%. The growth relationship of this species shows positively allometry, which means that this species could be a potential fish for future aquaculture.