The effects of different levels of protein and probiotics offered before and after weaning on growth performance, blood metabolites, and rumen fermentation were investigated in two experiments. In Exp. 1 (the pre-weaning phase), twenty-four single lambs, 10 days of age with an average live body weight of 15.3±1.8kg, were individually penned and randomly assigned to the treatments in a 2×2 factorial arrangement of protein levels (16% vs. 18% CP of DM) and probiotic levels (0 vs. 2g Protexin®/d). The diets consisted of 20% lucerne hay and 80% concentrate (on a DM basis) offered over a total of 60days including 15days of adjustment period and 45days of experimental period until weaning. The lambs were transferred to separate pens where they were allowed to suckle their respective dams twice a day (in the morning and in the evening). The experimental procedure in Exp. 2 (the post-weaning phase) was the same as that in Exp. 1 except for the protein levels (14.5% vs. 16.5% CP of DM) administered and the lucerne hay (30.0%) included in the diets. Twenty-four 78-days-old lambs, weighing 30.5±2.6kg, were individually penned and offered the diets for 60 days inclusive of 15 days of feed adjustment. The results of Exp. 1 showed that raising the protein content of the diet from 16% to 18% CP led to increased weaning weights (28.2 vs. 32.4±1.83kg; P<0.05), average daily gain (ADG) (288g/d vs. 381±19.4g/d; NS), and feed intake (490g/d vs. 541±19.4g/d; P<0.05). However, no significant differences were observed in food conversion ratio (FCR; P>0.05) among the treatments. BUN concentration was on the 18% CP diet (14.3mg/dl vs. 17.4±0.50mg/dl; P<0.05), and on diets without probiotics compared to those with probiotics (15.0mg/dl vs. 16.7±0.50mg/dl; P<0.05). Probiotic supplementation increased feed intake (485g/d vs. 546±19.4g/d; P<0.05) and rumen NH3-N (7.13mg/dl vs. 8.39±0.19mg/dl; P<0.05) during the pre-weaning period. Cortisol concentration was significantly lower (P<0.05) in lambs fed the probiotic significantly lower in the 16% CP diet than that supplemented diets than in those fed probiotic-lacking diets 24h after weaning (17.3mg/dl vs. 16.6±0.21mg/dl) and 48h after weaning (16.8mg/dl vs. 15.9±0.21mg/dl). In Exp. 2, final weight, ADG, feed intake, and FCR were not significantly different among the diets with different protein levels or between those with or without probiotic supplementation. In addition, feeding diets with the lower CP level (14.5% vs. 16.5%; DM basis) resulted in lower concentrations of blood metabolites, urea nitrogen (19.9mg/dl vs. 25.0±1.16mg/dl; P<0.05), rumen pH (5.99±vs. 6.22±0.03; P<0.05), and ruminal NH3-N (10.99mg/dl vs. 11.22±0.03mg/dl; P<0.05). It was concluded that the higher protein level (18% CP; DM basis) fed during the pre-weaning phase led to increasing feed intake and weaning weight compared to the lower CP diet (16%) but that a higher level of protein in the post-weaning diet (16.5% vs. 14.5% CP; DM basis) did not affect performance. Supplementing the diets with probiotics might have reduced stress (lower cortisol concentration) after weaning but it did not improve the performance of the lambs.