Descriptive morphological and morphometric characters for 45 parameters and weight-length relationship of 30 tropical freshwater bagrid catfish, Bagrichthys macropterus (Bleeker, 1853), from the Mun river in northeastern Thailand were investigated. The aim of this study was to quantify morphological differences between Bagrichthys macropterus and B. obscurus Ng, 1999. The results revealed that fin spines for the anal, caudal, dorsal, pectoral, and ventral fins were ii-iv/11-13; 8/7; I,7; I,7-8; and I,5, respectively. And gill rakers were 7-10. Serrations of the dorsal and pectoral spines were 13-15, 22-25, respectively, on posterior margin. Mandibulary teeth were not found on all tooth-bearing surfaces. All four pairs of barbel were longer in males than in females (P<0.05). Morphologically, this species is very similar to B. obscurus, but can be differentiated by caudal peduncle depth, nasal barbel length and serrations of the dorsal and pectoral spines. © Central Fisheries Research Institute (CFRI) Trabzon, Turkey and Japan International Cooperation Agency (JICA).