Technical Abstract: Sixteen lactating organic Jersey cows were assigned to four replicated 4 × 4 Latin squares with a 2 × 2 factorial arrangement of treatments to compare the effects of feeding cornmeal (CM) or molasses (MOL) with either flaxseed meal (Flax) or a protein mix [(PM = 11% soybean meal (SB) + 5% sunflower meal (SM)] on milk yield and N utilization. Cows were fed (% diet DM) grass baleage (70%), mineral pre-mix (2%), plus one of four concentrates (28% diet DM): 1) 12% CM plus 16% PM (CMP); 2) 12% CM plus 16% Flax (CMF); 3) 12% MOL plus 16% PM (MOLPM); or 4) 12% MOL plus 16% Flax (MOLF). Cows were fed twice a day with concentrates top-dressed on the baleage. Preplanned orthogonal contrasts were used to compare the main effects of: energy source (ES = CM vs. MOL) and protein source (PS = SB + SM vs. Flax), and the ES × PS interaction. A significant PS was observed for milk yield with cows fed Flax diets producing the lowest amounts. Cows fed MOL diets had the lowest (P = 0.01) feed efficiency while those fed PM diets the highest (P less than 0.001). Significant PS effects were observed for yields and contents of milk fat and milk protein. A dilution effect possibly explains the reduced (P less than 0.01) milk protein content in cows fed CMP and MOLP. A significant ES × PS interaction was found for MUN with cows fed CMF showing the highest and cows fed MOLF showing the lowest values, indicating enhanced N utilization in the latter diet. Cows fed MOL diets had the lowest PUN showing improved N utilization. Increased PUN with PM diets can be explained by their slightly greater CP compared to Flax diets. Overall, diets containing Flax reduced yields of milk and milk components while those containing MOL improved N utilization in organic cows.