Aims Soil fauna is one of the major drivers of plant litter decomposition. This study aims to assess how soil fauna density and diversity may affect litter decomposition. Also, we assessed whether faunal communities inside the litterbags that are used to control the access of faunal groups or communities in ambient soils are better for predicting their effects on litter decomposition, given that soil fauna frequently move into and out of such litterbags. Methods To answer this question, we synthesized 5336 observations extracted from 46 publications to assess the effects of soil fauna communities, their density and diversity on the rate of litter decomposition ( k ) and litter mass loss. Results Results showed that (1) the presence of soil fauna significantly increased k by an average of 33.0% and that the effects were mainly controlled by initial litter concentrations of phosphorus and magnesium, (2) the density and diversity of soil fauna in litterbags significantly affected k and/or mass loss, but ambient communities had limited effects, and (3) the effects of soil fauna in litterbags on k were most significant during the early stages of decomposition (0 − 30% mass loss). Conclusions Our study clearly showed that litterbag communities were better for predicting the effects of soil fauna on litter decomposition, and that their effects were most significant during the early stages of decomposition. These results improve our ability to estimate the contribution of soil fauna in liter decomposition and the associated carbon and nutrient cycling.