A study was conducted in the Jammu district of J &K (UT) where R.S. Pura and Bishnah development blocks were selected randomly out of 20 development blocks falling in the district. The mustard crop is among the oldest cultivated plants in Civilization. Biologically, the mustard plants belong to Cruciferae and under the genus Brassica. The primary data on cost and returns were collected through the survey method by personally interviewing the respondents with the help of a pre-tested questionnaire. For computing the cost and returns, the concepts issued by Commission on Agricultural Costs & Prices (CACP) were used. The per hectare total cost of cultivation of mustard crop was worked out to be ` 33746.34,` 36975.67 and ` 37678.76 on marginal, small, and medium farms, respectively, with an overall average of ` 36523.75 per hectare. The per hectare gross returns for mustard cultivation on marginal, small, and medium farms were ` 46094.05, ` 51235.01 and ` 64747.22 resulting in a cost-benefit ratio of 1:1.50, 1:1.52, and 1:1.89, respectively, over cost C2. Overall, on all farms, the per hectare gross returns were ` 53953.98 with the cost benefit ratio of 1:1.72 over the exact cost.