Platinum nanoparticles (PNPs) are potentially useful for sensing, catalysis, and other applications in the biological and medical sciences. However, toxicity data on the PNPs are very limited. In this study, we prepared PNPs using $K_2PtCl_6$, (21 nm in phosphate buffered saline) and tested inflammatory responses in mice after a single intratracheal instillation. The concentrations of pro-inflammatory cytokines (IL-1, TNF-${alpha}$, and IL-6), TH0 cytokine (IL-2), TH1-type cytokine (IL-12), and TH2-type cytokines (IL-4 and IL-5) were increased in broncho-alveolar lavage fluid by PNPs. It was found that the induciton of TH2-type cytokines were higher than TH1-type cytokine on day 28 after instillation. TGF-${eta}$ was also significantly increased in broncho-alveolar lavage fluid during the experimental period. IgE level in serum was increased with the increase of B cells distribution. Intracellular level of glutathione (GSH) was diminished by treatment of PNPs. When the distribution of T cell subtype ($CD4^+/CD8^+$) was analyzed, the ratio was decreased. Gene expression of matrix metalloproteinases was found to be significantly increased on day 1. By histopathological examination, cell infiltration of macrophages and neutrophils was observed in lung tissue during the experimental period. Based on these findings, it is suggested that the exposure to PNPs may induce inflammatory responses in mice.