This study aimed to investigate how game-playing affected low- and high-anxiety students’ English vocabulary and content learning in a digital game-based learning (DGBL) environment. The participants were 132 fifth-grade English as a Foreign Language (EFL) students, divided into an experimental group using DGBL instruction (n = 68) and a control group using traditional instruction (n = 64). They were defined as low- and high-anxiety students based on the Foreign Language Classroom Anxiety Scale (FLCAS), with 38 low- and 30 high-anxiety students in the experimental group and 34 low- and 30 high-anxiety students in the control group. Data was collected from FLCAS, game-playing logs, pre- and post-tests, and an open-ended questionnaire. The results found that both low- and high-anxiety students benefited from a DGBL environment designed with game mechanics (game challenges, points, and comments) to improve their English vocabulary and content learning performance, with high-anxiety students making greater progress. In the DGBL environment, the game challenges for entertainment purposes motivated the high-anxiety students to engage in learning. The high-anxiety students’ confidence in learning was then enhanced through the points and positively encouraging comments, leading to active and repeated engagement in game-playing. This self-motivated learning facilitated the high-anxiety students’ English vocabulary and content learning performance. This study suggests that the gap between low- and high-anxiety students’ English vocabulary and content learning performance could be narrowed in a DGBL environment with game mechanics.