10.22376/ijpbs.2019.10.1.p1-12 Volume 5 Issue 1 2014 (January - March) β-Mannanases have number of industrial applications. One of the important application is in biobleaching of pulp, for which enzyme has to be thermo-alkali-stable and cellulase-free. In this work a new strain of lessThan i greaterThan Bacillus nealsonii lessThan /i greaterThan PN-11 was isolated which produces a cellulase free, thermo-alkali-stable mannanase. The mannanase production from this strain has been optimized using Response surface methodology. On optimization enzyme yield increased by 17.2 fold. The enzyme was applied on softwood pulp to evaluate its bleaching potential individually and in combination with xylanase. PN-11 mannanase was able to improve the pulp properties when applied individually. Moreover, siginificant reduction in kappa number (32.23%), increase in roughness of pulp surface and enhancement of brightness (16.39%) as well as viscosity (3.20%) could be achieved when PN-11 mannanase was applied in combination with xylanase which makes it a potential candidate for application of pulp biobleaching at industrial scale. PRAKRAM SINGH CHAUHAN, SANJEEV KUMAR SONI, PRINCE SHARMA, ARCHITA SAINI AND NAVEEN GUPTA Cellulase free mannanase, thermo-alkali-stable mannanase, Bacillus nealsonii, Response surface methodology, Pulp Biobleaching. 237-251