This current study aims to investigate the effects of L1 and L2 glosses on vocabulary learning and reading comprehension of Korean English learners by a quantitative meta-analysis. The 42 research findings in 15 papers were synthesized by calculating their mean effect sizes. The meta-analysis was conducted in terms of subjects, language used in glosses, types of dependent variables, etc. The results showed that the use of glosses in foreign language teaching had above the medium effect. It was also found that the effects on vocabulary learning were stronger than reading comprehension in both L1 glosses and L2 glosses.