tBacillus sp. CFR1601, isolated from decaying plant litter, produced an extra-cellular endo-mannanase (198.0 IU/g)under solid state fermentation (SSF) using defatted coconut residue as the prime solid substrate. In order toenhance endo-mannanase production, three component, five level central composite design (CCD) of responsesurface methodology (RSM) was used. Based on contour plots and variance analysis, optimum conditions for endo-mannanase production from Bacillus sp. CFR1601 were attained when defatted coconut residue was supplementedwith sesame oil meal (10.0, w/w), Tween-80 (0.2%, v/v) and inoculated with bacterial cells from log phase (12 hold; OD600 nm≈ 3.6). The empirical model developed through RSM brought about 4.04–4.39-fold (800.0–870.0 IU/g)improvement in endo-mannanase yield as compared to un-optimized growth conditions. Downstream processingof endo-mannanase from SSF media was carried out for the first time using polyethylene glycol (PEG)/salt aqueoustwo phase system (ATPS). ATPS system consisting of a combination of PEG 3350 12.0% (w/w), Na2SO412.0% (w/w),protein load 10.0% (w/w) and pH 5.0 resulted in one-sided partitioning of endo-mannanase towards bottom phasewith 3.8-fold purification and 95.4% recovery. Second stage ATPS with fresh top phase further improved purificationof endo-mannanase to 12.32-fold. Our overall results suggest a cost-effective and integrated process for productionand downstream processing of endo-mannanase.