This multicenter, double-blind, randomized, parallel-group, non-inferiority study compared the efficacy and safety of morinidazole with those of ornidazole in women with pelvic inflammatory disease. Women from 18 hospitals in China received a 14-day course of either intravenous morinidazole, 500 mg twice daily (n = 168), or intravenous ornidazole, 500 mg twice daily (n = 170). A total of 312 of 338 patients in the full analysis set (FAS) (92.3%) were included in the per protocol set (PPS) analyses, 61 (19.6%) of whom were included in the microbiologically valid (MBV) population. The clinical resolution rates in the PPS population at the test of cure (TOC, primary efficacy end point, 7-30 days post-therapy) visit were 96.86% (154/159) for morinidazole and 96.73% (148/153) for ornidazole (95% CI: -3.79% to 4.03%). The bacteriological success rates in the MBV population at the TOC visit were 100% (32/32) for morinidazole and 89.66% (26/29) for ornidazole (95% CI: -16.15% to 11.21%). Drug-related adverse events occurred less frequently with morinidazole (32.74%, 55/168) than with ornidazole (47.06%, 80/170) (p < 0.01). For women with pelvic inflammatory disease, twice-daily morinidazole for 14 days was clinically and bacteriologically as efficacious as twice-daily ornidazole for 14 days, while the former was associated with fewer drug-related adverse events than the latter.