Hydrazide self-assembling nucleating agent (HSNA) was introduced into poly (lactic acid) (PLA) to improve its crystallization behavior and then microcellular PLA-HSNA foams were prepared via supercritical CO2 foaming. With the increase of HSNA content, the average cell diameter of the foams decreased obviously, from 64.39 to 6.59μm, while the cell density increased up to nearly three orders of magnitudes, from 6.82×106 to 4.44×109 cells/cm3. Compared with neat PLA foam, PLA-3wt% HSNA showed a roughly 556% increase in compressive strength, exhibiting excellent compression resistance. Upon cooling, the peak intensity at 1758 cm-1 attributed to the gt conformation of PLA chains for PLA-2wt% HSNA was always higher than that of neat PLA, indicating that by the introduction of HSNA, higher population of gt conformer formed and thus lower energy barrier was required for the following formation of PLLA α-crystal. During the nucleation and crystallization, for PLA-2wt% HSNA, the characteristic peaks changed according to the order of 1456 cm-1> 921 cm-1> 1210 cm-1, suggesting that, PLA chains could nucleate without major adjustment of the main chain by the addition of HSNA. HSNA can precipitate prior to the crystallization of PLA and self-assemble into fibrillar networks, inducing the crystallization of PLA on their surface and resulting in the formation of “shish-kebab-like” structure. The crystallization temperature moved to lower temperature for PLA-HSNA, and the crystallinity was much higher than that of neat PLA. Addition of HSNA not only significantly promoted the CO2 solubility of PLA foam, but also improved the viscoelasticity of PLA significantly, and thus micron sized foams were obtained. Due to the microcellular structure and the formation of enhanced “shish-kebab-like” crystalline structure on the cell wall, high compressive strength was achieved for the foam.