Data mining consists of evolving set of techniques that can be used to extract valuable information and knowledge from massive volumes of data. This paper highlights the data mining techniques applied to mine a group of received staff petitions through staff complaint mechanism in UN organization in Gaza. Staff complaint mechanism (feedback mechanism) is a mechanism that supports the staff members. The employees send complaints / petitions that face them by filling the requested details including the request type (complaint, question, suggestion, others, beneficiary or not categorized) . The response unit receives the requests and categorize it, and finally prepares the reply then sends it back to the employee. The important thing is: after the employee receives the reply, the employee should indicate whether he/she is satisfied with it or not. So the period between request date and reply date may affects the feedback since the regular reply period must not exceed 7 days after receiving any request. In this paper we attempted to study and analyze the data received within 18 months. This data sample contains more than 6000 records that cover different employee requests types. Thus, we try to know the effects of delay of reply on the feedback received by complainant staff; furthermore, we need to know what kinds of staff that always ask questions and try to find the relationship between staff salary (according to grade) and nature of the request. Thus this paper gives insight on how data mining can be applied in finding the consequences of staff requests and needs and hence try to minimize these requests over the time.