A field experiment was conducted during the 2008/09 short rain season in three major agro-ecological zones of Bukoba and Missenyi districts, Tanzania. The agroecological zones were characterized as follows based on the amount of rainfall: high (≥1500 mm), medium (1200 mm) and low (800 mm). Objectives of the study were to investigate the diversity of bean landraces in the areas, assess the effect of environment on genotypes performance, determine relationship among plant characteristics and their contribution to seed yield. Thirty eight bean landraces were collected from farmers in the two districts and evaluated in three locations: ARI- Maruku, Kyema and Byamutemba in high, medium and low rainfall zone, respectively. A Randomised Complete Block Design was used with three replications. Data collected were: days to 50% flowering, days to 90% maturity, plant height, number of pods per plant, number of seed per pods, 100 seed weight, grain yield and disease reaction. Data analysis revealed significant variations among genotypes for all characters investigated and significant genotypes x environment interactions for yield and yield components. Environmental factors reduced seed yield by 76% and by 39% in low and high rainfall zones, respectively, compared to the medium rainfall zone. Kamoshi gave significantly higher seed yield across locations. Seed yield had positive highly significant correlations with pods per plant and seeds per pod. Path coefficient analysis showed that, seeds per pod contributed most to seed yield. Stability parameters estimates indicated that genotypes had significantly different seed yield performance across environments, suggesting for multi-location testing for seed yield. However, Kamoshi had seed yield stability across the environments. The study findings suggest existence of diversity among the bean landraces and that their responses differ with environments. Future studies should focus on genotyping of the landraces to determine the extent of their diversity and performance in diverse production environments.Ministry of Agriculture