A study was conducted during the winter seasons of 2003-04 and 2004-05 at the Agricultural Research Station, Mandor, Rajasthan to determine the effect of crop-weed competition on seed yield and quality of cumin (Cuminum cyminum L.). The results revealed that weed-free upto 60 DAS gave the lower mean weed density and total weed dry matter at harvest and increased yield attributes viz., mean final plant stand, umbels/plant, seeds/umbel and test weight by 157.9, 147.4, 166.2 and 37.2%, respectively, and mean seed yield by 788.7% over weedy check. This treatment stood at par with complete weed-free and weedy upto 15 DAS with regards to yield attributes and seed yield. The critical period of crop-weed competition was observed between 15 to 60 DAS in cumin. Weed-free environment throughout crop season produced the maximum oil and protein content, and was significantly higher compared to weedy check.