This book reports the results of an investigation done on assessing the effect of Waste Paper Sludge Ash (WPSA) as additive in cement mortar. WPSA from paper mill is used as partial replacement of ordinary Portland cement in mortar. The study involves four replacement levels of WPSA into OPC at 5%, 10%, 15% and 20%. Tests were conducted to explore the characteristics and properties of WPSA in mortar at fresh and hardened states. The mortar cubes were cast and were cured for 7 days, 14 days and 28 days to explore the strength development of the mortar. It is concluded that addition of WPSA at 5 percent of cement helps the mortar to achieve the higher compressive strength at 7 curing days. Use of WPSA is feasible to be used as an additive in mortar and would help to increase the compressive strength of mortar at early stage.