Using supercritical carbon dioxide (CO2) as the physical foaming agent, polylactic acid/poly(butylene succinate)/zinc oxide (PLA/PBS/ZnO) microcellular nanocomposites were prepared by batch foaming method. The effects of foaming temperature, holding pressure and depressurization rate on the microcellular morphology of PLA/PBS/ZnO microcellular nanocomposites during the supercritical CO2 microcellular foaming process were investigated. The results showed that the influence of foaming temperature on the microcellular morphology was mainly reflected in the melt strength. With the foaming temperature being too high or too low, well-distributed and dense microcellular could not be formed due to the change of the melt viscosity and surface tension. With the foaming temperature at around 90℃, the minimum average cell diameter, the maximum cell density, and the most concentrated distribution of microcellular were achieved. The effect of holding pressure on the microcellular morphology was confined to the solubility of the supercritical CO2 and the viscosity of foaming system. When holding pressure was too low, the large size and uneven distribution in microcellular were resulted. With the holding pressure being around 16 MPa, the maximum cell density, and the most concentrated distribution in microcellular were achieved. Depressurization rate determined the nucleation efficiency at the initial stage of foaming process. With the increase in depressurization rate, the average cell diameter decreased, while the cell density increased, with the increase in the number of cells, and more concentrated size distribution.