Abstract: Objective To evaluate the effect of serum luteinizing hormone (LH) variation on clinical outcomes in patients with polycystic ovarian syndrome (PCOS) undergoing in vitro fertilization-embryo transfer (IVF-ET). Methods A retrospective analysis was conducted in 314 patients with PCOS undergoing their first IVF cycle using standard long protocol. On the basis of LH concentrations on early-, mid- and late-follicular phase, the patients were divided into decreased LH (LH ratio≤1, group A) and increased LH (group B, LH ratio>1) groups in early- to mid-follicular phase, decreased LH (group C) and increased LH (group D) groups in mid- to late-follicular phase, and decreased LH (group E) and increased LH (group F, LH ratio>1) in earlyto late-follicular phase. The clinical outcomes were compared between groups A and B, groups C and D, and between groups E and F. Results No significant differences were found in the clinical outcomes between group A and B (P>0.05). The number of oocytes retrieved and the early abortion rate were significantly lower, but the normal fertilization rate, implantation rate, clinical pregnancy rate and ongoing pregnancy rate were significantly higher in group D than in group C (P<0.05). In group F, the early abortion rate was significantly lower and the ongoing pregnancy rate was significantly higher than those in group E (P<0.05), and no significant differences were found in other clinical outcomes between the two groups (P>0.05). Conclusion An increase in LH level from early- or mid- to late-follicular phase has a positive effect on the clinical outcomes, but this LH variation in early- to mid-follicular phase does not affect the clinical outcomes.