Objective: to detect optimum dose of vaginal misoprostol for cervical priming by comparing between two doses (200μgm and 400μgm vaginal misoprostol) prior to office hysteroscopy by 3 hours. Design: randomized controlled trial. This study done on 132 patients to whom done office hysteroscopy as a part of investigation of (primary infertility, secondary infertility, recurrent miscarriage or abnormal uterine bleeding) .those patients divided into two groups each group 66 patient, Group I, received 200μgm vaginal misoprostol dissolved in saline 3 hours before office hysteroscope and group II received vaginal 400μgm vaginal misoprostol dissolved in saline 3 hours before office hysteroscope. Our Main outcome measures was pain score (visual analogue scale), ease of entry (Likert scale), procedural time in seconds, patient acceptability (Likert scale) and also to detect side effects of misoprostol and complication of its use. Result: in group II which received 400μgm vaginal misoprostol, pain score was lower (3.45± 1.372) compared to group I (5.36± 1.260). procedural time shorter in group II (98.94 ± 18.389)than group I(134.15 ± 27.083) , cervical entry was easier in group II(4.02 ± 0.832) than group I (2.98 ± 0.540), patient acceptability was higher in group II(3.53 ± 0.638) than group I(3.03 ± 0.495) which received200μgm vaginal misoprostol. No complication detected in both groups. Side effects were minimal and transient. Conclusion: use of 400μgm vaginal misoprostol 3 hours before hysteroscopy is better than 200μgm vaginal misoprostol in facilitating cervical ripening with minimal side effects without use of anasthesia.as it decrease pain score, decrease procedure duration, increase ease of cervical entry, higher patient acceptability and with minimal side effects.