Effective use of construction material is profitable in the industry as well as in the economy of any country. This research is aimed to cause of material wastage and rank highly wasted construction material on public building projects in western Oromia. The result of the study analyses, mostly causes of construction materials are; Changes made to the design while construction is in progress, Lack of attention paid to dimensional coordination of products, Damage during transportation, Improper planning for required quantities, Designer’s inexperience in method and sequence of construction. In addition, causes of construction material wastages are presented under seven attributes causes. As well as wastage of material on eight key construction, material are ranked as concrete, wooden formwork, block, and steel are most wasted by asking respondents based on their experience in the construction industry. Generally, wastage of material is highly occurred in every activity i.e. during design, construction and during the production of the material.