The welding fume has been implicated as a causal agent in respiratory disease such as pneumoconiosis. The molecular mechanism by which welding fume induces toxicity in the lung is still unknown, but studies have focused on histological structure and indirect approach measuring the pulmonary damage markers. In the present study, gene expression profiles were analyzed in the lung of rats exposed by manual metal-arc stainless-steel (MMA-SS) welding fume for 30 days using Affymetrix GeneChip$^{(R)}$. Totally, 379 genes were identified as being either up- or down-regulated over 2-fold changes (P<0.01) in the lung of low- or high-dose group and were analyzed by using hierarchical clustering. We focused on genes involved in immune/inflammation responses were differentially regulated during lung injury induced by welding fume exposure. The information of these deregulated genes may contribute in elucidation of the inflammation mechanism during lung injury such as lung fibrosis.