The process parameters of ATPS were varied to in order to enhance the purification fold of endo-mannanase. PEG 3350 12.0% (w/w), Na2SO4 12.0% (w/w), protein load 10.0% (w/w) and pH 5.0 resulted in optimum one-sided partitioning of endomannanase towards bottom phase with 3.8-fold purification and 95.4% recovery.