Because the implant is regarded as a common treatment. It is clinically important that systemic and local risk factor of threatening peri implant mucosa should be considered during the process. The most risk factors are detected in clinical diagnosis, but it might be difficult and not clear to recognize systemic or combined factors. This article reviews risk factors of peri-implantitis. Local factors are biomechanics, periodontal soft tissue characteristics, infected site and oral hygiene. Systemic factors are alcohol, smoking and genetic traits.