Objective The aim of this study was to investigate the serum levels of mild, severe preeclamptic pregnants and normotensive pregnant women to determine whether there is a correlation between preeclampsia and their serum levels. Methods This prospective case-control study included 48 preeclamptic and 39 healthy normotensive pregnants. The control group was composed of body mass index and age matched pregnant women. Preeclamptic patients were divided into two groups as mild preeclampsia and severe preeclampsia. Serum apelin levels were determined by EnzymeImmunometricAssay (EIA) biochemical test. Results Serum apelin levels were found to be significantly lower in the preeclampsia group. It was 0.75 +/- 0.24 ng/ml in mild preeclampsia and 0.55 +/- 0.18 ng/ml in the severe preeclampsia and 0.91 +/- 0.20 ng/ml in the control group. There was a strong inverse correlation between serum apelin levels and Systolic Blood Pressure (SBP) (r: -0.429p: 0.002). Conclusions In conclusion, the role of apelin and apelinergic system in cardiovascular system and placental development and their place in preeclampsia is still an issue. In preeclampsia, the deterioration of the cardiovascular protective effect of apelin by other enzymes may also contribute to the deterioration of fetal development. More detailed studies are needed.