Fisherman at District of Jember had not been enjoyed profit yet because there was restrictiveness to access market opportunities, such as low productivity, low quality of product, low price and low support from corporate world. This study purposed: (1) to determine market structure of sea fish; (2) to know performance of marketing channel and to analize marketing margins of sea fish at Jember. In order to achieve those puposes, we used quantitative and qualitative descriptive through survey techniques, accidental and snowbolling sampling according to the type of population being sampled. There were two types of population in this study, they were fisherman and marketing agencies which were involved. Data collected by Indepth interviews and observation techniques and analyzed by descriptive analysis, marketing margins and elasticity of transmission price. The results were: 1) The market structure of sea fish at Jember lead to market Monopolistic Competition (between perfect competition and monopoly); 2) there were five pattern of marketing channel of sea fish at Jember and all were running inefficiently because of elasticity of transmission price was less than one; and 3) Marketing margin of sea fish at Jember reached Rp 14,550, - per kg, which share of marketing costs only 10.96%, share of marketing profit reached 61.79% and share of margin which was received by fisherman 27.25% (<50%), it meaned marketing of sea fish in study area run inefficiently.