Abstract: Genotype x environment interaction limit the effectiveness of selection when selection is based only on mean yields. This study evaluated eight mustard (B. juncea) cultivars and breeding lines of Oilseed Research Programme at ten different agro-ecological zones during winter 1997-98 and 1998-99. The significant GxL interaction caused difficulty in identifying superior yielding mustard genotype. Therefore, stability parameters in addition to mean seed yield over environments were calculated. The analysis of variance indicated that heterogeneity of regressions was highly significant (P<0.01). The overall yield performance of the KS-74, CV-3 and BARD-1 genotypes was superior. Genotypes KS-74 and CV-3 had b-values near to one and low deviations from regression indicating relatively stable performance over environments. The lowest b-value of BARD-1 indicated that it performed relatively better in low yielding environments and less well adapted to favorable environments. The result of this investigation demonstrated that production response index (regression coefficient) and other stability parameters are suitable means of selecting cultivars that are stable, high yielding and responsive. It is Further illustrated that the regression coefficient is the most useful stability statistics, which can be applied for the selection of brassica cultivars adapted to wide range of environments or adapted to restricted environments.