Dusky-gilled mudskipper Periophthalmus variabilis, a member of the family Gobiidae, is a potential aquarium pet in the Mekong Delta (MD), Vietnam; however, data on its feeding habit and intensity has been limited. Therefore, this study aims to evaluate the relative gut length (RGL) and gastro-somatic index (GI) of Periophthalmus variabilis in order to determine the feeding habit and intensity of this mudskipper and its variation regarding sex, size, season, site, and their interaction. One thousand one hundred seventy mudskipper samples were collected monthly in four locations: Duyen Hai-Tra Vinh, Tran De-Soc Trang, Hoa Binh-Bac Lieu, and Dam Doi-Ca Mau from January 2022 to December 2022. The analysis showed that Periophthalmus variabilis was a carnivorous fish with an average RGL value of 0.52±0.01 SE (