The purpose of this study was to investigate the influence of metacognition on learning flow of high school students, and the mediating effect of self-directed learning ability. To accomplish this purpose, a total of 216 first grade high school students in Chungbuk were sampled. The instruments used for the study were Metacognition Scale, Self-Directed Learning Scale, and Learning Flow Scale. Structural equation modeling(SEM) using AMOS 7.0 was employed to examine the relationships. The major findings were as follows; First, the hypothetical model was fitted to the empirical data(χ2=195.642, df=83, p=.000, RMSEA=.079, GFI=.896, TLI= .936, CFI=.949, NFI=.916). Second, metacognition had direct effects on self-directed learning ability and learning flow, and self-directed learning ability had a direct effect on learning flow. In addition, metacognition had an indirect effect on learning flow using a mediating variable(self-directed learning ability). The findings of the study suggested the importance of metacognition development program to facilitate self-directed learning ability and earning flow.