This paper aims to recognize the effect of material waste on cost increase in Palestinian construction projects. The study used questionnaire survey to achieve its objectives. The target population of the study are constructors and consultants involved in construction projects. The study also predicts the effect of cost overrun on material waste in some construction activities, namely: ceramic and brick works. The collected data were analyzed using statistical analyses. The study has established that among the various factors that affect cost overrun, experience in the line of work, conflicts among project participants, payments delay, and political situation are the key factors. While the analysis revealed that the main material waste factors are: poor site management, using untrained labors, rework due to workers' mistakes, selecting the lowest bidder contractor/subcontractor, and frequent change orders. Data from 55 building projects constructed in the West Bank between 2015 and 2020 were collected to test the relation between material waste and cost increase. Two mathematical models were developed: Model (l) links cost increase and waste in ceramic works. It indicates that if waste increases by 1%, the cost will increase by 1.07%. Model (2) links between cost increase and material waste in brick works. It tells that if waste increases by 1%, cost will increase by 1.25%. R square of value >0.7, for both models, indicates a strong linear relation between cost increase and material waste. This is the first study that predicts the effect of material waste on cost increase in Palestinian construction sector. The study encourages different parties related to construction projects to manage factors of cost overrun and material waste to enhance the sector of construction.