Chronic formaldehyde inhalation studies have suggested its relativity to teratogenicity, cancer incidence, neurodegenerative and vascular disorders. Many toxicological data on the formaldehyde toxicity are available, but proteomic results showing complete protein profiles are limited. Therefore, alterations of protein expression patterns upon formaldehyde treatment were investigated in the human lung epithelial cell line. Differentially expressed proteins following formaldehyde treatment were analyzed on 2-dimensional gels, and further analyzed by MALDI-TOF to identify the proteins. Among the identified proteins, 24 proteins were notably up-regulated and 6 proteins were down-regulated. In particular, cytoskeleton related protein named vinculin and Rho GDP dissociation inhibitor which plays a key role in apoptosis increased remarkably.