Abstract: In order to study the selectivity of Scomberomorus niphonius gillnet mesh systematically,four different meshes of 110,115,120 and 125 mm were tested during fishing operation from April to May 2013.Selectivity model curves and body shape coefficients were used to analyze the mesh selectivity.Results showed that ①The gillnet tested had good selectivity,the dominant species were Scomberomorus niphonius and Sebastes fuscescens with IRI values of 18 626.8 and 2 740.1,respectively.②Gamma model obtained the best goodness-of-fit with the selectivity model curves among the common models tested.③The formulae describing the relationship between mesh size(α)and fork length(l)or body weight(W)were α=0.092 7l and α=4.59W^1/3,respectively.④The formula describing the relationship between mesh size and maximum perimeter of body section(S)was α=0.224S-5.37.⑤The optimum meshes for catching 3-4 ages of S.niphonius were estimated to be 120.4 and 121.5 mm respectively by Gamma selective curve and the afore-mentioned formulae.The optimum meshes for different ages of S.niphonius were also calculated based on the historical fishing data.