The problem of misspelled Thai words written in social media is increasing rapidly by youth in Thailand. To decrease the number of misspelled Thai words and improve the learning achievement for Thai youth, a firstperson 3D mobile game was developed. The game is run on an Android smartphone applying a gyroscope sensor. This game has 3 levels in 5 stages. The learning achievement is evaluated from 37 players' pre and posttest scores, who are bachelor's degree students of Animation and Game, College of Arts, Media and Technology, Chiang Mai University, Thailand. The data were statistically analysed by a paired sample ttest. Pre and posttest scores were weakly and positively correlated (r = 0.666, p < 0.001). There was a significant average difference between pre and posttest scores (t36 = 11.776, p < 0.001). On average, posttest scores were 15.027 points higher than pretest scores (95% CI [17.615, 12.439]). The results of the research show that the gamebased learning approach significantly improved players' learning achievement in misspelled written Thai words.