Aim Recent studies suggest that apelin can be a novel potential therapeutic mediator to improve the diagnosis, and treatment of preeclampsia. This study aimed to investigate the association of serum apelin-13 and apelin-36 with preeclampsia and to detect their relationship with preeclampsia-associated perinatal morbidity. Methods Forty-four women with preeclampsia were included as the study group. Forty-four healthy pregnant women, at similar gestational week with similar gravidity, formed the control group. The clinical findings, biochemical indicators, maternal and perinatal outcomes, and the serum concentrations of apelin-36 and apelin-13 were evaluated. The levels of apelin-13 and apelin-36 were determined with commercial kits using a competition-based enzyme-linked immunosorbent assay method. Results The mean gestational age at sampling was 35.77 +/- 2.515 weeks in the preeclamptic group, 36.45 +/- 2.057 weeks in the control group (P = 0.270). Maternal serum apelin-36 and apelin-13 concentrations were significantly lower in patients with preeclampsia compared to the individuals in the control group (P = 0.030 and P = 0.005, respectively). The optimal cut-off points of apelin-36 and apelin-13 measurements for discriminating between preeclampsia and controls were evaluated by the receiver-operator curve analysis. The results showed that apelin-13 and apelin-36 are moderately successful markers to differentiate subjects with preeclampsia from healthy pregnant women. The concentrations of apelin-13 and apelin-36 in both groups were not statistically different in cases with and without adverse fetal/neonatal outcomes. Conclusion In conclusion, we investigated serum apelin-13 and apelin-36 concentrations in preeclamptic patients and demonstrated markedly lower maternal concentrations compared to healthy pregnant women.