Floristic study and variation in frequency, density and basal cover of crop and weeds were studied at bimonthly intervals in a mixed wheat and mustard crop at Gujar lake margin in district Jaunpur (Uttar Pradesh). The total number of weed species recorded on 28th December, 2008 and 27th February, 2009 were 34 and 37, respectively. Maximum number of weeds was of Poaceae and followed by Asteraceae. Cynodon dactylon was the most dominated weed. The maximum frequency (65 and 72%), density (54.19 and 99.80/m2) and basal cover (1.084 and 2.994 cm2/m2) were of Cynodon dactylon followed by Cyperus rotundus. It was mainly due to their vegetative mode of propagation and by their competitive ability in the favourable soil moisture, texture and nutrients conditions.