Drought is a major yield-limiting factor in maize production. Osmotic stress was applied to two maize inbred lines with polyethylene glycol 6000 treatments. Proteins from the leaves were analyzed by two-dimensional gel electrophoresis and peptide mass fingerprinting at two time points, 24 and 48 h after osmotic stress. Thirty-five proteins were differentially expressed between control and treatment groups in the two maize inbred lines. In ‘Qi319’, a drought-tolerant inbred line, there were five up-regulated proteins at 24 h and 13 up-regulated and one down-regulated protein at 48 h. In drought-sensitive line ‘Zheng58’, 10 proteins were up-regulated at 24 h, while six proteins were up-regulated at 48 h. The 35 proteins were subjected to mass spectrometry and 17 proteins were successfully identified. These proteins were classified into six categories: photosynthesis-related, energy and metabolism, signaling pathways, protein synthesis, defense-related, and unclassified.