This study is a double blind clinical trial, and our goal is determining the effect of vitamin D supplementation on the occurrence of preeclampsia in pregnant women, who have a history of preeclampsia, previously. The participants are pregnant women, referred to the Besat clinic in Sanandaj city, who are enrolled in the study with informed consent. By using random assignment and table of random numbers, each patient is assigned to the intervention group or control group. Patients and researchers are unaware of the allocation of each patient. The number of participants is 142, this study is a single-center study and the third phase of clinical trial. Every two weeks, 50,000 units of vitamin D Perl is given to the intervention group, and placebo given to the control group. Zahravi pharmaceutical company is manufacturing the drug and placebo. Inclusion criteria is, having a history of preeclampsia, and blood level of vitamin D above 32 nanograms per milliliter following 12 hours of fasting, measured by Lieberman Bouchard method. The intervention is prescribing, Vitamin D. The main outcome is preeclampsia. Measurable variable of preeclampsia is, recording of sitting blood pressure above or equal to 140/90 mm Hg, and proteinuria in the urine test, is higher or equal to +1. Blood pressure every two weeks is measured in both groups. If blood pressure be equal or greater than 140/90 mm Hg, urine tests will be requested.