The present study has been estimated the population biological parameters of Ambassis vachellii living in Bay Hap (BH) and Cua Lon (CL) estuarine regions. By analyzing the results of length-frequency distribution of 6,922 individuals (4,388 individuals in BH and 2,534 individuals in CL), collected from August 2017 to June 2019, it was concluded that  L_∞ of these two populations was 7.4 cm and K value of BH population (0.58 yr^-1) was higher than that of CL population (0.52 yr^-1). Moreover, the t₀ value of the CL population (-0.44 yr^-1) was higher than that in the BH population (-0.39 yr^-1). The fishing (1,38 yr^-1), natural (1,76 yr^-1), and total mortalities (3.14 yr^-1) of the BH population were lower than those of the CL population, which were 1.90 yr^-1, 3.08 yr^-1, and 4.98 yr^-1, respectively.  Accordingly, the longevity of the former population (t_max=5.17 yr) was lower than the later one (t_max=5.77 yr).  Likewise, the population growth performance was 1.50 in BH and 1.46 in CL. The CL population's recruitment time (mid-May and mid-August) was a month later than the BH one (mid-April and early July). The exploitation rate (0.440 in BH and 0.620 in CL) was higher than E_0.5 (0.353 in BH and 0.355 in CL). Results suggested that these two populations were subjected to overfishing. The length at first capture was 3.3 cm in BH and 3.4 in CL. Consequently, it is recommended to avoid catching A. vachellii during the recruitment period for sustainable fishery management.