A factorial experiment (3×2) was conducted to investigate the influence of feeding diets containing three crude fiber levels (12.52, 14.51 and 16.51%) with or without (0.0 or 0.03%) a probiotic supplementation  on performance, nutrient digestibility, carcass traits and blood constituents of growing New Zealand White (NZW) rabbits. A total of 72, six-week-old NZW rabbits were individually weighed, randomly divided into 6 equal experimental groups, each with four equal replications, and kept at battery cages in a naturally-ventilated house. All groups of rabbits were reared under similar hygienic and managerial conditions. Six experimental diets were formulated and used during the experimental period from 6 to 12 weeks of age. Performance were evaluated in terms of live body weight, daily weight gain, daily feed intake, feed conversion ratio,  protein efficiency ratio, efficiency of energy utilization and performance index. Digestibility of nutrients [dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), crude fiber (CF) and nitrogen-free extract (NFE)], carcass traits (relative weights of carcass, total edible parts and abdominal fat) lengths stomach, caecum and small and large intestines, and some blood plasma constituents (glucose, cholesterol, triglycerides, total protein, albumin and globulin) were also determined. The results obtained can be summarized as follows: Growth performance, carcass traits and lengths of alimentary tract segments, blood constituents were not significantly affected by dietary crude fiber level or probiotic supplementation. Increasing dietary crude fiber level from 12.5% to 14.5 or 16.5% decreased the digestibility of DM, OM and NFE but significantly improved CF digestibility for 12-week-old NZW rabbits, while the digestibility of CP and EE was not affected. Dietary supplementation with probiotic had no significant effect on the digestibility of nutrients, with the exception of a significant improvement in CP digestibility compared with that of the control rabbits. The interactions between dietary fiber level and probiotic supplementation were not significant for all criteria examined in the present study. Based on the obtained results, it is concluded that the optimal level of dietary crude fiber for fattening rabbits to achieve maximal growth rate and best efficiency of feed utilization is 12.5%.