Preeclampsia is one of the most common causes of maternal and neonatal morbidity and mortality worldwide. We aimed to evaluate the diagnostic values of maternal serum levels of 25-hydroxyvitamin D and paraoxonase 1 (PON1) and neutrophil to lymphocyte ratio (NLR) in the preeclamptic patients and to assess whether they can be used to distinguish the severity of preeclampsia. This prospective study was conducted in women with preeclampsia (n=34) or severe preeclampsia (n=10) and normal pregnancies (n=36), with at least gestational age of 24 weeks. Maternal serum 25-hydroxyvitamin D and PON1 were measured and NLR was calculated. The 25-hydroxyvitamin D levels of the study groups were found comparable (P > 0.05). The normal pregnancy and preeclampsia groups were comparable (P > 0.05) with regard to the PON1 level; however, their PON1 levels were significantly higher compared to the severe preeclampsia group (P < 0.05). The NLRs of the normal pregnancy and preeclampsia groups were found similar (P > 0.05), but the NLR of severe preeclampsia group was significantly higher compared to the normal pregnancy and preeclampsia groups (P < 0.05). The maternal serum 25-hydroxyvitamin D level is not useful as a marker in the diagnosis of preeclampsia; however, the maternal serum PON1 level and NLR may distinguish the patients with preeclampsia with severe features, but not the patients with preeclampsia without severe features.