This study set out to investigate the relationship between L2 vocabulary knowledge (VK) and second-language (L2) reading/listening comprehension. More than 100 individual studies were included in this meta-analysis, which generated 276 effect sizes from a sample of almost 21,000 learners. The current meta-analysis had several major findings. First, the overall correlation between VK and L2 reading comprehension was .57 (p < .01) and that between VK and L2 listening was .56 (p < .01). If the attenuation effect due to reliability of measures was taken into consideration, the 'true' correlation between VK and L2 reading/listening comprehension may likely fall within the range of .56-.67, accounting for 31%-45% variance in L2 comprehension. Second, all three mastery levels of form-meaning knowledge (meaning recognition, meaning recall, form recall) had moderate to high correlations with L2 reading and L2 listening. However, meaning recall knowledge had the strongest correlation with L2 reading comprehension and form recall had the strongest correlation with L2 listening comprehension, suggesting that different mastery levels of VK may contribute differently to L2 comprehension in different modalities. Third, both word association knowledge and morphological awareness (two aspects of vocabulary depth knowledge) had significant correlations with L2 reading and L2 listening. Fourth, the modality of VK measure was found to have a significant moderating effect on the correlation between VK and L2 text comprehension: orthographical VK measures had stronger correlations with L2 reading comprehension as compared to auditory VK measures. Auditory VK measures, however, were better predictors of L2 listening comprehension. Fifth, studies with a shorter script distance between L1 and L2 yielded higher correlations between VK and L2 reading. Sixth, the number of items in vocabulary depth measures had a positive predictive power on the correlation between VK and L2 comprehension. Finally, correlations between VK and L2 reading/listening comprehension was found to be associated with two types of publication factors: year-of-publication and publication type. Implications of the findings were discussed.