Abstract: An investigation of the physical, chemical and microbial population changes that occurred during the composting of water hyacinth was carried out. After 11 weeks of composting, the compost turned black, had decomposed and had no smell. The pH was 7 and the highest temperature reached, of 40°C occurred in the first week. The initial carbon/nitrogen ratio was 17.61 and this increased to 18.12 by the end of the composting. The coliform population declined greatly from 8.11 to 5.85 MPN (log)/g and fecal coliforms and Escherichia coli were not detected in the final product. Bacteria were the dominant microbes in the compost followed by actinomycetes and fungi. Mesophillic microorganisms were present in higher numbers than thermophillic microorganisms throughout the composting. The highest cellulase and xylanase activities in the compost of 6.67 and 10.24 U/kg DW, respectively were detected in the second week which was related to the temperature. Bacillus sp. strain B4 was isolated and investigated for cellulase and xylanase using agro-industrial residues as substrates during Solid-State Fermentation (SSF) processes. Corncob and rice straw were good substrates for the production of the enzymes with a maximum cellulase of 1.19 U/gDW and xylanase activity of 2.54 U/g DW, respectively. The activities of both enzymes were stable and maximum at 50°C. This study indicated that agro-industrial residues should be mixed with water hyacinth for composting to facilitate the development of a thermophilic phase during the composting process and to improve the product. Bacillus sp. strain B4 can be used as a starter strain.