Length-weight relationships (LWR) were estimated for three main Songkhla Lagoon fish species occurring in the lower gulf of Thailand. Samples were collected monthly during monsoon and after monsoon season (September 2017 to April 2018). Fishes were captured by three methods: fishing gear, crab gear and shrimp gear. This study is the first reference on LWR equation parameters of Pellona ditchella (Valenciennes, 1847), Sardinella gibbosa (Bleeker, 1849) and Alepes vari (G. Cuvier, 1833) in the lower gulf of Thailand, this good document would be used to compare these fish condition with many coastal areas in the world. This work provides the important information of fish migration between lagoon and lower gulf of Thailand as well as for two species from which we present a wider size range in FishBase, Pellona ditchella (Valenciennes, 1847) and Sardinella gibbosa (Bleeker, 1849).