The aim of this study was to report the size structure of finescale razorbelly minnow, Salmostoma phulo in the Payra River, Southern Bangladesh, based on length-frequency distribution (LFD), sex ratio (SR), length-weight relationships (LWR), length-length relationships (LLR), condition factors (allometric K_A; Fulton’s, K_F; relative, K_R and relative weight, W_R) and form factor (a_3.0). A total of 306 individuals ranging from 6.00–10.70 cm in total length and from 1.26-9.20 g in body weight were collected using traditional fishing gear from January 2014 to November 2014. The overall sex ratio of the species did not reveal significant variation from the expected value of 1:1 (χ² =0.32, p<0.05). The allometric coefficient b calculated for the LWR based on various dimensions indicates both sexes grew allometrically (negative for males: b<3 and positive for females: b>3). Moreover, the values of b for LWR, LLR and condition factors did not differ significantly (p>0.05) between the sexes of S. phulo. The estimated value of W_R was very close to 100 indicating the balanced habitat with available food relative to the presence of predators. To the best of our knowledge, this is the first inclusive and comprehensive explanation on the size structure of S. phulo from Bangladesh and it should be crucial for the sustainable management of this SIS fishery not only in southern coastal waters of Bangladesh but also in all of its geographical distributions including India and Myanmar.