The purpose of this study was to compare the efficiency of slow freezing with that of vitrification method for the cryopreservation of human embryos. Human embryos were derived from in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) and the mixed solution of propanedial (1.5, 1.0, 0.5M PROH) and sucrose (0.1M), ethylene glycol (7.5, 15%), dimethyl sulfoxide (7.5, 15% DMSO), sucrose (0.5, 1.0M) and SPS (Serum Protein Substitute) was used for a cryoprotectant for slow freezing and vitrification solution, respectively. Rates of recovery after thawing, morphological normality, post-thaw viability, arrest, morphological abnormality and preimplantation development were compared between two protocols. After freezing-thawing, recovery and survial rate of slow freezing was (88.6% and 73.4%), whereas vitrification was (99.2% and 96.2%) (p<0.05). The arrest rate of slow freezing was significantly lower compared with those of vitrification(8.7% vs 29.9%) (p<0.05). Preimplantation development to the 2-cell (83.8% vs 67.7%), 4-cell (69.0% vs 47.2%) and 8-cell (62.4% vs 37.8%) stages 24, 48 and 72 h after thawing, respectively, were higher in the slow freezing than the vitrification. After slow freezing and vitrification of human embryo at 2-8cell stage, the rate of recovery rate, survival rate and partial damage rate were 92.0% vs 100%, 80.4% vs 96.2% and 52.2% vs 19.0%, respectively. And partial damage rate was significantly lower than those of slow freezing method (p<0.05). These results demonstrate that a slow freezing using PROH is more efficient than a vitrification for cryopreserving the human zygotes, although the vitrification yielded better recovery, survival and partial damage of frozen-thawed 2-8 cell stage embryos than slow freezing method.