The effect of propionic acid on fermentation and aerobic stability of whole-plant maize silage was evaluated using laboratory silos. Whole-plant maize silage was treated with 2 1/tonne propionic acid; silage with no additives served as the control. The results showed that application of a low rate of propionic acid could influence the ratio of organic acids and reduce NH(3)-N in fermentation and improve aerobic stability by 40 h in maize silage. It also accelerated yeast multiplication at the early stage of fermentation but restricted it at the late stage.