An expert is a person of law , he is the specialized professional and assistant judicial whose service is indispensable for both community and judiciary, thus this study is highlighting the legal nature of civil liability of an expert whether contractual or default liability and the legal basis for each of them .It also highlight the elements of this liability, impacts and ways of compensation. Finally, this study dealt with provisions of civil liability of an expert in terms of means of defense and extent of agreement on strictness or exemption and mitigation and the extent of insure civil liability of an expert. This study shown several results summarized as follows: 1. Civil liability of an expert (default or contractual) is subject to general rules of civil liability. 2. Different of consultant expert liability from judicial expert. 3. Compensation dealt with direct damage only and subject to court discretion. 4. Government is committed to compensate errors of party expert only. 5.Expert insurance of his work to ensure remedy of damages to third parties.