Reinforced concrete is one of the most widely used items in construction projects. Wastes of construction materials have been recognized as a significant problem for different stakeholders involved in construction projects. Material waste affects the efficiency and productivity of construction projects negatively, especially the reinforced concrete materials as it represents a large portion of most construction projects' costs. This paper aims to identify and analyze the main causes of the reinforced concrete materials waste (RCMW) in the Egyptian construction projects from the point of view of contractor and consultant site engineers. A literature review was conducted to gather a list of causes contributing to the RCMW. The resulting 23 causes were categorized into four groups; design, material management, labor, and site management. The resulting list of RCMW causes was subjected to a questionnaire survey for quantitative analysis and identification of the most important causes of RCMW from the point of view of contractors and consultants. The analysis of variance (ANOVA) and paired-samples t-test were used to study the effect of participants’ experience on their scoring. The experience relative importance index (ERII) of these causes was calculated to assess their effects on RCMW. The overall results indicated that the most ten important causes of RCMW are: lack of on-site material control, lack of supervision, poor coordination, design change, over procurement (unused materials), rework due to worker's mistake, waiting for resources, selection of unsuitable material, material storage, incorrect materials (wrong procurement).