Maternal mortality rate (MMR) in Indonesia is still high. One of the causes of MMR in Indonesia 2010- 2013 was hypertension in pregnant (preeclampsia). Effect of preeclampsia was a complication for mother and baby. One of the mechanisms of preeclampsia was immune response, there were natural killer cells which induced inflammation. PIBF was a pregnancy protector factor by inhibiting NK lymphocytes and increasing anti- inflammation. Mild regular exercise induced IL6 to make IL10 higher. This research's objective was to analyze serum PIBF level because of mild regular exercise in Mus musculus as endothelial dysfunction model induced preeclampsia. This research was true experimental using post test only with control group design. This research consisted of 4 groups: K1 (normal pregnant mice), K2 (endothelial dysfunction model), K3 (endothelial dysfunction model with mild regular exercise since early pregnant), and K4 (endothelial dysfunction model with mild regular exercise since 1 week before pregnant). The exercise used a treadmill without angle for 18 minutes once in 2 days for 2 weeks. The results were serum PIBF level in K1 was 11,982 ng/ml, in K2 was 11,609 ng/ml, in K3 was 7,256 ng/ml, and in K4 was 19,731 ng/ml. Data distribution was not in normal, so data were analyzed by Kruskal Wallis Test with α=0,05. The result was no significant differences of serum PIBF level (p=0,076). The conclusion was mild regular exercise had not increased serum PIBF level yet significantly.