The primary aim of this paper was to investigate the relationship between self-regulated learning and English academic achievement in high school students, and to analyze the relative effects of the former variable on the latter. In addition, a gender difference in self-regulated learning was examined. The research subjects consisted of 246 students (123 boys and 123 girls) sampled from four high schools. The statistical methods for data analysis were correlation technique, multiple regression analysis, and ANOVA. The major findings of this research were: (a) There was a positive correlation between the two main research components - the achievement score was positively correlated with cognitive regulation (r=.21, p<.05) and motivational regulation (r=.23, p<.05); (b) The most contributive variable to English academic achievement was the self-efficacy of motivational regulation; and (c) Girls have appeared to rely on their cognitive strategies more than boys in school learning activities.