Rapeseed has been introduced in the cropping systems in west of Iran during last decade. It is expected to affect weed species composition especially those from Brassicaceae family. A weed survey was conducted in rapeseed fields in west of Iran during spring 2017. Totally 50 fields in 5 regions (10 per region) were chosen for sampling. At each field, one phytocoenological relevé plot) of 50 m² was recorded in the field center. Weed species, altitude, pre-crop, production area and locality were recorded. The coverage of species was estimated using nine degree Braun-Blanquet cover-abundance scale. Monitoring was performed during the spring 2017 before weed control operations. The data were processed using multivariate analyses in the Canoco for Windows 4.5. As explanatory variables the locality, pre-crop (barley, wheat, coriander), altitude and production area (ha) were chosen. As dependent variables species cover data were used. Statistical analysis showed that the locality and pre-crop are the significant explanatory variables affecting weed species distribution. Totally 19 species were found. Sinapis arvensis, Avena ludoviciana, Convolvulus arvensis, Galium tricornutum, Vicia villosa, Lathyrus sp, Lactuca Serriola, Fumaria vaillantii, Erigeron Canadensis, Erodium cicutarium, Malva neglecta and Carthamus oxyacantha were found as the most frequent species. In terms of species cover, S. arvensis followed by A. ludoviciana and C. arvensis were found as the most dominant species.
