Abstract : Several issues arise that can’t be resolved during the execution of a project. Such problems typically include contractor requests for extension of time or an additional cost, or both. When the contractor requests them, they are called claims. The issue is sorted if the owner accepts the contractor claim and grants him extension of time or additional cost, or both. If owner does not agree to the contractor claim and there are various interpretations, the claim becomes a dispute. To avoid or reduce claims in the construction projects it is required to investigate the causes of claims. This study aims to understand of causes of the claims in the building projects in Egypt in an attempt to enable practitioners to be familiar with claims to avoid or minimize when they occur. From international literature, factors that cause claims were identified then modified by expert questionnaire to be suitable to Egyptian construction. Then the factors were subjected to questionnaire to identify their importance. The responses were analyzed by spearman coefficient, Cronbach's alpha variable, k-s test, and one sample t-test. To analyze the collected data of the research, Statistical Package for the Social Science (SPSS) were used. The most prevalent causes of claims that were deduced.