The study was aimed to assess the factors influencing waste generation in buildings project in southwestern, Nigeria. The study randomly sampled 261 professionals through a questionnaire survey. Tables and figures were used to present the collected data and ranking and percentage were used to analyze the data collected. It was revealed that Design (Frequent design changes and poor design) lack of early contractor involvement, last-minute client requirement, engagement of inexperience designer, undefined project brief, poor design quality are the most important factors that influence l waste generation during buildings project. It was recommended that site operatives and craft men should be equipped with waste minimization knowledge, they should carry along in every management decision regarding waste management plan development as a major player on sites.