Objective To observe whether the increase of oxidative stress in PC12 cells could influence the levels of protein carbonyls and nitrotyrosine and alter the cytoskeleton and cell morphology under clinostat condition,and whether the increase of content of nitrate/nitrite in cell culture medium could influence the cell proliferation and differentiation.Method Cell morphology,carbonylated actin and nitrotyrosinated tubulin,and mRNA and protein express of nNOS and iNOS were observed and determined with immunofluorescence and RT-PCR technology in clinostat rotated and control static groups.At the same time,cell density was measured and cell cycles were detected with flow cytometry.The relationship between all these changes and NOS were also analyzed.Result The levels of carbonylated and nitrotyrosinated cytoskeleton protein were altered,no obvious changes in cell morphology but neurite outgrowth after on a clinostat rotation.Cell density also increased significantly,DNA synthesis in cell cycles was shortened.Conclusion All of these results indicate that simulated weightlessness do not alter cell morphology and is beneficial to the growth of PC12 cells.The mechanism involved may be associated with the increase of NOS activity.