Objective: To evaluate the efficacy of misoprostol used in first-trimester abortion in obese women and to determine whether obesity is associated with time to a successful medical abortion. Methods: The records of patients diagnosed with missed abortion at our clinic between 2018 and 2021 were retrospectively reviewed. All women aged 18 to 45 years who were diagnosed with missed abortion in the first trimester and treated with misoprostol were included in the study. The cases were divided into two groups: obese (body mass index [BMI] ≥ 30 kg/m2) and non-obese (BMI < 30 kg/m2). First, they were simultaneously administered 200 μg misoprostol orally and 400 μg vaginally. After the first misoprostol administration, the dose was repeated vaginally at 400 μg every three hours if necessary. The effect of obesity on the time taken to achieve a medical abortion was evaluated. Results: A successful medical abortion occurred in 45.2% of the women in the obese group and 69.0% of those in the non-obese group. The time to uterine evacuation was 8.24 ± 4.03 h in the obese group and 6.35 ± 3.54 h in the non-obese group. The relationship between obesity and time to a successful medical abortion was evaluated using the Kaplan–Meier curve, which showed a significant difference between the two groups (p = 0.028). Conclusion: Our findings show that obesity affects time to a successful medical abortion. In addition, the rate of successful medical abortion after misoprostol administration was lower in the obese women.