Security is one of most important issue in network management and detection of intrusion based security attacks play vital role in it. To have a holistic picture of the network intrusion detection, selection of appropriate feature is very important; it reduces analysis effort and time too. Identification of most astute feature for attack classification plays significant role in intrusion detection. Data mining can be very fruitful for feature selection and intrusion detection. In this paper, KDD '99 intrusion detection dataset is evaluated to find out most important and relevant features.