The marketing of milk and milk products by dairy plants of co-operative and private sectors in Tamil Nadu has been compared. The study is based on the data collected for toned milk, standardized milk, full cream milk, flavoured milk, butter and ghee from the selected co-operative and private dairy plants of the Coimbatore district for the financial year 2001-2002. It has been found that the marketing cost for toned milk is same in both the dairy plants , whereas it is higher for standardized milk, full cream milk and flavoured milk in the co-operative dairy plant. The marketing cost has been found less in the cooperative plant for products like butter and ghee . All the dairy products earn more marketing margins in the private than co-operative dairy plant, except for toned milk .The marketing efficiency of cooperative dairy plant for all dairy products has been observed relatively less than that of private dairy plant, except toned milk .The study has suggested the development of co-operative dairy industry in a sustainable manner, the co-operative dairy plants should formulate long-term vision and strategy. The study has observed that value addition in dairy products should be done without compromising the quality and consumer-oriented market research and development should be accorded greater attention .