METHODS: RAW264.7 cells were incubated with 200μg/ml silica for indicated times (0, 6, 12, 24, 48h). The morphological changes of cells were observed by transmission electron microscopy (TEM). Real-time PCR and Western blot were performed to detect the protein expression of BiP and CHOP. DAPI staining, Flow Cytometry (FCM) and Cleaved caspase-3 were used to measure apoptosis. In the prevention experiments, the ERS inhibitor 4-PBA was used to inhibit ERS and evaluate the changes of cell apoptosis.