This paper introduces quasi-maximum likelihood estimator for discretely observed diffusions when a closed-form transition density is unavailable. Higher order Wagner-Platen strong approximation is used to derive the first two conditional moments and a normal density function is used in estimation. Simulation study shows that the proposed estimator has high numerical precision and good numerical robustness. This method is applicable to a large class of diffusions.Keywords Quasi-maximum likelihood estimator, diffusions, Wagner-Platen approximation. * The author thanks a co-editor and three referees for outstanding comments and suggestions. Thanks also go to Eckhard Platen, Yongjun Tang, and seminar participants at the SNDE 17th annual symposium for helpful comments. All remaining errors are mine.