Background: Missed abortion occurs when the deceased result of conception remains in the uterus beyond 20 weeks of gestation. Misoprostol, a prostaglandin analogue, is often employed for medical purposes. Objective: The aim of this study is to investigate whether change in the acidity of the vagina affects the pharmacokinetics of the misoprostol and, therefore, its efficacy for mid-trimester abortion induction Methodology: The study is a prospective study conducted on a cohort of 81 pregnant women (gestational age 14-26 weeks and failed abortion) at the obstetric department of Al-Zahra university hospitals in the interval from August2021 till February 2022 they were followed up for 24 hours. Results: Induction abortion intervals were substantially longer in group  with pH ≥ (5) than in group with pH < (5) (22.33± 2.29 hrs. vs. 11.80± 1.63 hrs. p < 0.001).  Group pH ≥ (5) showed an increased prevalence of fever and intense abdominal pain compared to group < (5) (p < 0.001 & 0.007 respectively). Conclusion: Misoprostol used vaginally for inducing of mid-trimester abortion is more effective when vaginal acidity is increased as it was more effective in group pH < (5).