The main aim of the present study was improving the nutritional values of corn stalks as an example of poor quality roughage and to improve its utilization by animals. Therefore, sixty-four New Zealand White rabbits of five weeks old were randomly distributed into four groups of sixteen rabbits each. The animals of the first three groups were fed on rations contained corn stalks treated biologically with Trichoderma viride (T. viride), with 10%, 20% or 30% respectively. whilst those of the fourth group were given ration without T. viride (0%, eg. the commercial diet). At the end of the experimental period. which lasted for 12 weeks three rabbits from each treatment were selected and slaughtered to study the different carcass characters. All the results were subjected to analysis of variance. The most important results obtained in the present study could be summarized as follows: 1- It was observed that replacement of berseem hay by biologically treated corn stalks at different levels did not affect statistically on daily body weight gain. On the other hand, daily feed consumption had been affected significantly by treatment differences. 2- It was noted that replacement of berseem hay by biologically treated corn stalks at different levels may improve feed conversion values. 3‘ The results of slaughter weight (SW), carcass weight (CW), empty body weight (EBW) and dressing percentage (DP) were not significantly affected by replacement of berseem hay by biologically treated corn stalks. 4- Marked differential effects due to different biological treatment had been observed on weights and percentages of testis relative to carcass weight and empty body weight. 0n the other hand. results of the other edible organs did not show any significant effects due to biological treatment. 5- Weights and percentages of different carcass cuts (fore legs, thoracic cage, loin and hind legs) were not influenced by dietary treatments. 6- Crude protein and ash percentages of L. dorsi muscle were not influenced statistically by the biological treatment differences. On the other hand, the dietary treatments affected significantly dry matter and ether extract contents. Finally, based upon the present results, it could be suggested that T. viride can be used safely to enrich poor quality roughages such as corn stalks, and that fungus (T. viride) can be used successfully to improve the utilization of untraditional rabbit feed stuffs. Likewise, upon the basis of the present investigation, it could be stated that the biological treatments of rabbit rations can be used safely without adverse effect on growth performance and health of animals. So. it can be recommended as it is easy to be applied by farmers.