Microbial xylanases that are thermostable, active at alkaline pH and cellulasefree are generally preferred for biobleaching of paper pulp.. We screened obligate and facultative marine fungi for xylanase activity with these desirable traits.Several fungal isolates obtained from marine habitat showed alkaline xylanase activity. The crude enzyme from NIOCC isolate # 3 (Aspergillus niger) with high xylanase activity, cellulase-free and unique properties containing 580 U L -1 of xylanase, could bring about bleaching of sugarcane bagasse pulp by a 60 min treatment at 55 o C, resulting in a decrease of 10 kappa numbers and a 30% reduction in consumption of chlorine during bleaching process. The culture filtrate showed peaks of xylanase activity at acidic pH (3.5) and alkaline pH (8.5). When assayed at pH 3.5 optimum activity was detected at 50 o C with a second peak of activity at 90 o C. When assayed at pH 8.5 optimum activity was seen at 80 o C. The crude enzyme was thermostable at 55 o C for at least 4 h and retained about 60% of the activity. Gel filtration of the 50-80% ammonium sulfate precipitatedfraction of the crude culture filtrate separated into two peaks of xylanase having specific activities of 393 and 2457 U mg -1 protein. The two peaks showing xylanase activities had molecular masses of 13 and 18 kDa. Zymogram analysis of xylanase of crude culture filtrate as well as the 50-80% ammonium sulphateprecipitated fraction showed two distinct xylanase activity bands on native PAGE The crude culture filtrate also showed moderate activities of -xylosidase and -L-arabinofuranosidase which could act synergistically with xylanase in attacking xylan. This is the first report showing potential application of crude culture filtrate of a marine fungal isolate possessing thermostable, cellulase-free alkaline xylanase activity in biobleaching of paper pulp.