Three independent studies using male Kajli lambs at post-weaning, growing and finishing stages were designed and undertaken to examine the effect of different protein sources with or without probiotics on growth performance and carcass characteristics. In the trial I, 32 male Kajli lambs at three months age were randomly divided into eight groups of four animals each in a 4×2 factorial arrangement. Four iso-caloric (70% TDN) and iso- nitrogenous (22% CP) diets were formulated with four different protein sources i.e. corn gluten meal 30% (CGM), canola meal (CM), cotton seed meal (CSM) and sunflower meal (SFM) containing either 0 or 50g of probiotics (Protexin®)/ ton of feed. In trial II and III, lambs were again randomized and given the same treatment as in trial I. However, crude protein (CP) content of diets was reduced from 22 to 18% in trial II and 18 to14% in trial III. In trial I, higher (P<0.05) dry matter (DM) and CP intake, DM, CP, neutral detergent fibre (NDF) and acid detergent fibre (ADF) digestibility, blood glucose, N-balance and total weight gain were observed in lambs fed CM diet than those fed CGM, CSM and SFM diets. However, blood urea nitrogen (BUN), creatinine and serum minerals remained unaltered (P>0.05) in lambs fed diets containing different protein sources. Neutral detergent fibre and ADF digestibility and blood glucose was higher (P<0.05) in lambs fed diets containing probiotics. Dry matter and CP intake and their digestibility, BUN, creatinine, serum minerals, N-balance and total weight gain remained unaltered (P>0.05). In trial II, higher (P<0.05) DM and CP intake, blood glucose, N-balance and total weight gain were noticed in lambs fed CM diet than those fed CGM, CSM and SFM diets. However, diets containing different protein source didn’t affect (P>0.05) the DM, CP, NDF and ADF digestibility, BUN, creatinine and serum minerals. Neutral detergent fibre and ADF digestibility and total weight gain was higher (P<0.05) in lambs fed diets containing probiotics. However, diets containing probiotics didn’t influence (P>0.05) DM and CP intake, DM and CP digestibility, BUN, blood glucose, creatinine, serum minerals and N-balance. In trial III, higher (P<0.05) DM and CP intake, N-balance and total weight gain were observed in lambs fed CM diet than those fed CGM, CSM and SFM diets. However, DM, CP, NDF and ADF digestibility, BUN, blood glucose, creatinine and serum minerals remained unaltered (P>0.05) in lambs fed diets containing different protein source. Acid detergent fibre digestibility and total weight gain was higher (P<0.05) in lambs fed diets containing probiotics however, DM and CP intake, DM, CP and NDF digestibility, BUN, blood glucose, creatinine, serum minerals and N- balance remained unaffected (P>0.05). Hot carcass weights of lambs differed significantly (P<0.05) in lambs fed diets containing different protein sources with or without probiotics. However, dressing percentage (DP) and skin, feet, heart, liver and lungs weight remained unaltered (P>0.05) across all the treatments. The higher DP was observed in lambs fed CM diets, whereas it was lower in lambs fed SFM diet. Leg, loin, shoulder, breast and neck weights of the half carcass of the lambs remained unaffected (P>0.05) across all the treatments. Crude protein content of carcass was different (P<0.05) in lambs fed diets containing different protein source with or without probiotics, while moisture, ether extract and ash contents remained unaltered (P>0.05) across all treatments. The ratio of lean, fat and bone in primal cuts of half carcass (neck, shoulder, breast, loin and leg) remained unchanged (P>0.05) across all the treatments, except for the proportion of lean in shoulder, bone in loin and fat in legs, which was affected (P<0.05) by the diets containing different protein sources. In short, the lambs fed CM diets performed better than those fed CGM, CSM and SFM diets in all the three trials. Diets containing probiotics improved weight gain in trial II and III but not in trial I.