Abstract: In order to evaluate biologic effects of mixed culture of canola-field bean on farming system, in comparison with sole cropping, an experiment was carried out in 2004 at Ramin Agriculture and Natural Resources University, Iran. Experimental design was randomized complete blocks with three replicates. Different compositions of two crop, canola and field bean are treatments of the experiment, that including 20, 40 shrub m-2 for canola and 0, 20, 40 and 60 shrubs m-2 for field bean. Grain yield and components of crops, weed biomass and diversity, Land Equivalent Ratio (LER) and dominance index were evaluated. Results showed a significant difference between sole cropping and mixed culture in grain yield and components. In canola mixed field bean, yield of both crops was lower than monoculture. Highest yield of canola in monoculture was gained with 40 canola shrubs m-2 (2788 kg ha-1) and lowest grain yield was gained with intercrop of 40 and 40 canola and field bean shrub m-2, respectively. This trend, also be observed in field bean yield with increase of intercrop composition. It seems that cause of yields loss is competition between two crops and decrease of branches. Highest LER was found in mixed 20 and 60 canola and field bean shrub m-2, respectively. And lowest LER was observed in mixed 40 and 20 canola and field bean shrub m-2, respectively. Lowest dry matter (DM) of weeds within mixed stands was gained with 20 canola and 40 field bean shrub m-2. Highest DM of weeds was related to monoculture of 20 canola shrub m-2. Also, with increase density of field bean mixed stands, DM of weeds decreased, significantly. Also, diversity of weeds was decreased in mixed stands, in comparison with monoculture.