In order to analyze three-dimensional (3-D) slope stability, new 3-D methods are proposed by extending the simplified Bishop method, the simplified Janbu method and Spencer's method to three dimensions. It is shown that these methods are more accurate and reasonable than 3-D simple slice method proposed in the authors' previous study. Next, the approximate equations of 3-D safety factors for 3-D simplified Bishop method and Janbu method are presented and their limits of applicability are discussed.