Copper powder with different size was synthesized using subcritical/supercritical mild alcohols without additional reductant. The interaction influence of the reducing atmosphere, including temperature, pressure, precursors, and alcohol types, was investigated. XRD and SEM were applied to analyze the composition and morphology of products synthesized. Results showed that the reducing atmosphere formed by critical conditions, precursors, and mild-alcohol types had a significant effect on the products. The reducing atmosphere could be enhanced obviously with higher temperature and pressure. CuO was easier to reduce than Cu(NO3)(2) and CuSO4 under the same conditions. Compared with ethanol, methanol could form a stronger reducing atmosphere at the same temperature and pressure. Supercritical methanol (250 degrees C, 9 MPa) with CuO as a precursor could provide the optimal reducing atmosphere for the synthesis of copper powder. In addition, it was proposed that mild alcohols should play an important role as capping agents as well as reducing agents under subcritical/supercritical conditions.