This experiment was conducted to study the effect of using biological treatment by (Trichoderma reesei), to reduce the content of antinutritional factors in watermelon vines and improvement their nutritive value and the possibility of using it in animal nutrition and its effect on productive performance of growing lambs. Fifty male Barki lambs at 6 to 8 months of age with an average live body weight 24.49 ±0.2 Kg were divided into five similar groups according to their live body weight (10 lambs for each).  They were randomly assigned to receive the five experimental rations where control group was fed 50% concentrate feed mixture  (CFM) plus 50%  berseem hay (BH ) on dry DM basis (R1) and the other four groups R2, R3, R4 and R5 were fed rations containing 25 or 50 % untreated watermelon vines  hay (WMVH) and treated with Trichoderma reesei fungi (WMVF), respectively. Animals were fed the five respective rations in groups. The growth experiment lasted for sex months. Results showed that degradation of antinutritional factors was more efficient when WMV hay biologically treated with fungi (Trichoderma reesei).The values of antinutritional factors of the watermelon vines reduced as follows: total phénols by 53.43%, total tannins 71.38%, saponins 63.67%, alkaloids 44.02% and flavonoids  16.98%, compared with untreated vines. Control ration (R1) and the tested ration (R4) had higher DM intake than the other tested ones (R2, R3 and R5), being ration R3had the lowest value. Animal fed R4 showed more soluble, degradable, less undegradable fractions and more effective degradability. The values of final body weight, total body weight gain and daily gain were significant lower for tested rations R2, R3 and R5 than those of control one (R1), while the tested ration R4 was similar in these values with those of control one, being the highest values among all tested rations. The feed conversion as (g DMI/g gain) was worse with all tested rations related to that of control one, whereas R4 had the best feed conversion value among all tested ones. The values of feed conversion recorded 6.93 and 7.05 for R1 & R4 and 8.22 & 8.73 for R2 and R5, respectively, while the worst value was recorded with R3 (8.96). The feed cost was decreased by 11.98 and 25.62 for R2 & R3 (rations which contained 25 or 50% untreated watermelon vines) and 11.78 & 24.59 for R4 and R5 (rations which contained 25 or 50% watermelon vines treated with fungi) respectively, compared with the figure of control one (R1). The economic efficiency improved by 23.64% for R4 compared with control group (R1) and the other tested rations (R2, R3 and R5). The results could be indicated the possibility of introducing biologically treated watermelon vines with fungi in growing lambs rations up to 25% (i.e. 50% in replacing of berseem hay) to reduce the feed costs without harmful effects on their performance and health.