Onion and Potato seed are mainly supplied by community based seed production and marketing cooperatives in Ethiopia. The problem of seed marketing which faced the onion seed producer and marketing cooperatives of Mech wereda of Amhara regional state is the major reason to undertake this study. The study tried to analyze the performance of the three onion seed producing and marketing cooperatives of the wereda. The objectives of the study are to analysis the capacity of the cooperatives to make reasonable profit and produce quality seed. Assessing the main factors for members` participation in their cooperatives and identifying their main challenges and opportunities are also main objectives. These objectives serve as indicators for the general performance of the cooperatives in running the seed business. The research used descriptive statistics, financial profitability ratios and binary logistic regression model; - to assess members` socio economic, demographic, institutional factors, profitability status, factor for members` participation in cooperatives and describes seed quality status. Questionnaires, interview schedule and focused group discussion sessions were run to get the primary data. 120 member farmers and 30 nonmember farmers were the respondents for the research from six kebeles. Data collection was done from December 2017 to February 2018. The study indicated that the cooperatives are weak in making profit from the seed marketing due to their poor involvement in onion seed distribution and supply of other inputs. The cooperatives are found good in producing quality seed and the participation of members in governing their cooperatives is also found to be high. 75 % of the respondents are active participants, which indicate the high acceptance of the cooperative by their members. Regarding factors that influence on extents of members` participation 16 variables were identified out of which 7 were found to be significant. These are duration as membership, access to information and training, dividend obtained, communication channels used and satisfaction on cooperatives management. Total cultivated land holding was also found important to influence members` participation. Economically members` participation is found to be high in input purchase but low in supplying the produced onion seed to their cooperatives and in purchasing additional shares. Reduction in seed sales volume was found to be the key challenge, which needs to be tackled through improving the current seed distribution channels, demand estimation information and providing good stack holder support. The cooperatives should be equipped with appropriate postharvest implements and also their access to credit should be improved to make them competent in seed marketing. Key words: seed producer cooperatives, participation, onion seed