Objective. To determine placental gene expression of calcitonin generelated peptide (CGRP), calcitonin receptor-like receptor (CRLR), receptor activity modifying protein 1 (RAMP1), and endothelial and inducible nitric oxide synthases (eNOS and iNOS) in mild preeclampsia, and to assess the effects of magnesium sulfate (MgSO 4 ). Methods. Term placentas were obtained from 10 normotensive (NT group), 10 preeclamptic (PE) patients treated with 0.9% NaCl solution (PES group), and 8 PE women who received MgSO 4 (PEMgSO 4 group). The levels of mRNA were evaluated by real-time PCR. Results. Placental gene expression of CRLR, RAMP1 and iNOS were significantly higher (p < 0.001) in the PES group than in the NT group, without changes in CGRP. In addition, eNOS expression was 67% lower (p < 0.001) in the PES group. When compared with the PES group, the PEMgSO 4 group showed significantly higher expression (p < 0.05) of CGRP, CRLR and eNOS, while iNOS was significantly lower (p < 0.05). Conclusion. Placental gene expression of CRLR, RAMP1 and iNOS is higher in preeclampsia than in normal pregnancy, and MgSO 4 treatment increased CGRP and CRLR and presented opposite effects upon eNOS and iNOS.