Abstract: In order to evaluate plant density and cultivar effects on grain filling rate and duration, yield and its components of 3 pinto bean cultivars a factorial experiment (using RCB design) was conducted in 2007 at agricultural and natural resources research institute in East Azerbaijan province (Tabriz/Iran). Three cultivars (Khomeyn, G -14088 and 11816) were planted at 4 densities (14, 20, 30 and 60 plants m-2) in 3 replications. A 2-part linear model was used to quantifying the grain filling parameters. Interaction effect of cultivar and plant density affected Grain Filling Rate (GFR), Mass Maturity (MM), Maximum Grain Weight (MGW) and Effective grain Filling Period (EFP) significantly. Highest amount of these parameters observed at Khomeyn cultivar in 14 plants m-2. These parameters decreased in Khomeyn and G-14088 cultivars with increasing in plant density significantly. Between cultivars and plant densities treatments of pinto bean was significant difference in yield and its components. But interaction effect of cultivar and plant density affected only days to maturity, number of pod per plant, 100 seed weight and grain yield parameters. These parameters (except grain yield) decreased with increasing in plant density. But increasing of plant density and number of pod in square meter compensated reduction of yield components. Therefore, grain yield increased with increasing in plant density. Khomeyn cultivar had maximum amount GFR, MGW, EFP, number of pod per plant, 100 seed weight and grain yield. Therefore, Khomeyn and 30 plants m-2 are best cultivar and plant density in pinto bean, respectively.