A Survey of weed flora of Indian mustard (Brassica juncea L.) in south-western Haryana conducted during 2004-05 revealed that a total of 29 species were found to infest mustard fields, out of which 3 were grassy, 26 were broadleaf weeds. Asphodelus tenuifolius Chenopodium album, Melilotus indica, Trigonella polycerata, C. murale, Cynodon dactylon, Orobanche aegyptiaca, Carthamus oxycantha, Avena ludoviciana and Convolvulus arvensis were found highly associated with mustard crop in all districts. Asphodelus tenuifolius was the dominant weed in all districts except Hisar where relative density (R.D.) of C. album was more. Malwa parviflora a robust dicotyledonous weed which was considered to be weed of non cropped areas has also shown its presence in Jind, Jhajjar, Hisar, Rohtak and Mewat districts. Infestation of parasitic weed Orobanche aegyptiaca was more in Bhiwani, Rewari, Mahender Garh, Jhajjar and Gurgaon districts where crop is grown in light textured soils( loamy sand) and irrigated by sprinkler.