This study was carried out to investigate the ecotoxicological response on Gammarus sobaegensis Ue´no with acid stress. Mean value of LT_50(lethal time 50%) under pH 3 condition as acute ecotoxicity test was observed to be 0.271(±0.146) day. And 0.812(±0.377) day under pH 4, respectively. Mean value of LT_50 under pH 3 and 5 were 6.313(±0.828), and 9.475(±4.881) day, respectively. Variance in chronic ecotoxicity test pH(F ratio: 11.240, P<0.0005) and times(F ratio: 2.916, P<0.005) as single factor were revealed to be the major factor for determining LT_50 with acid depression. The variation of secondary gill surface with acid stress to be certain that wrinkle phenomenon. Being weak tolerance of G. sobaegensis against the acid stress, it shows the possibility to be examined as an aquatic toxicity test organism.