In this study, we investigated and identified criterial human factors(errors), most of which lead to terrible ship accidents such as collisions, sinking, fire and explosions resulting both in human lives and physical damages to ships as well as surrounding environments. To this end, we went through the accident reports of 413 cases over 2005~2009 period and classified the human factors into 6 major factors with 19 sub ones which were constructed in hierarchical order. The relative importance of major factors was calculated and among others the lack of awareness turned out to be the most important factor with the weight of 0.391. The contributions of the results in the research are two fold: it will help (i) identify the root causes of ship accidents and prevent further potential ship related incidents, (ii) analyze the degree of the risk associated with the ship accidents, when risk analysis is performed.