The present study was carried out in the Central Laboratory for Food and Feed (CLFF) to study the effect of treated rice straw and cotton stalks with white-rot fungi (Pleurotus ostreatus) alone. added yeast (Saccharomyces Cervisiae), incubated yeast for 15hr and combination of fungi and yeast on chemical composition, fiber fractions, digestibility of dry matter (IVDMD), digestibility of organic matter (IVOMD). true digestibility (lVTD), pH and microflora of ruminal fluid (Enterococci count, lactic acid bacteria count and total anaerobic bacteria oount).The results of chemical composition showed in case of RS incubated with 80 tor 15hr increase in protein content (from 4.6 to 6.2%). and in case CS incubated with 80 for 15hr (from 3.5 to 5.9%) however. additional increase in case of spent FiC (from 4.6 to 7.6%) and spent OS (from 3.5 to 10.9%). The results of fiber content were decrease in general, in case of HS incubated with SC for 15hr decrease in fiber content (from 34.8 to 33.4%). and in case of CS incubated with 80 for 15hr (from 48.2 to 45.9%). However, additional decrease in case of spent FiC (from 34.8 to 16.4%) and spent CS incubated with 80 (from 48.2 to 30.9%). Each of fiber fraction. lignin content in both experimental materials showed considerable decrease refers to the treatment with fungi or yeast or both. The result of IV-DMD showed highest value with the treated rice straw with fungi + yeast (52.24%) and the same trend with IV-OMD (60.54%). However. the highest lV—true digestibility value was with treated rice straw with fungi and incubated yeast for 15hr (66.28%). No effect of yeast treatment on the pH value of the rumenal fluid over all the experiment. The administration of SC to small ruminants stimulates the growth of the beneficial rumenal bacteria which consequently positively affects the rumenal fiber degradation i.e someEl vs. 56x103.30x103 vs. same“ and 20x103 vs. 52x103 for enterococci count. lactic acid bacteria count and total anaerobic bacteria count, respectively. The results revealed that the cultivation of fungi and inculation or addition with yeast could improve the nutritive value of rice straw and cotton stalks. Hence, the biological treatment, in addition, of sharing it for improvement of nutritive value of these residues to be suitable for animal feeding, the treated residues share in reducing the environmental pollution by avoiding burning it.