Labour share of income in developing economies has generally declined with increased engagement in international trade, raising concern about adverse distributional consequences of trade for workers. Using a panel dataset of Indonesian manufacturing firms from 1990 to 2015, we evaluate how trade affects the dynamics of labor share from a micro-level perspective. We find that trade liberalization contributes to declining labor share, mainly by shifting market share towards better-performing firms with already-low labor share. While this is in line with the superstar firm framework, such model fails to characterize the labor share dynamics in a developing economy like Indonesia where aggregate markups and concentration do not rise. Instead, this study supports a trade-based explanation for labor share decline.