Abstract Body: Preeclampsia is a hypertensive disorder that originates from the placenta and increases the risk of adverse outcomes in pregnancy. Highly elevated plasma and placenta leptin levels are characteristics of preeclampsia, and we have shown that leptin infusion in pregnant mice induces key characteristics of preeclampsia including endothelial and placental dysfunction. Notably leptin increases mitochondrial uncoupling in the placenta. We hypothesized that leptin infusion in pregnancy induces mitochondrial dysfunction in the placenta. We infused timed-pregnant C57/Bl6 mice with saline (sham) or leptin (0.90mg/kg/day) via s.c. osmotic minipump from gestation day (GD)11-18 (n=4). We sacrificed on GD18, recorded the dam’s weight and litter size and weighed the placentas before using them for mitochondrial analysis. To measure mitochondrial function, we isolated the mitochondria from the placenta and performed amplex red assay to measure hydrogen peroxide production and TMRM assay to measure membrane potential. We also assessed mitochondrial morphology via electron microscopy (EM) on whole placenta sections. Briefly, approximately 15-20 high magnification slides were taken per placenta and mitochondria were visualized, traced, and their area, circularity and density measured via FIJI ImageJ. All statistics performed were student’s t-test. Our data show that leptin did not change mitochondrial hydrogen peroxide production (2550±628.4 sham vs 3551±1001 leptin, p=0.15, a.u./mg of protein) or membrane potential (278.6±109.5 sham vs 401.9±123.3 leptin, p=0.29, a.u./mg of protein) compared to the sham placentas. Leptin increased mitochondrial number (5.085±0.47 sham vs 6.053±0.97 leptin, *P<0.05, count), matrix density (131.5±4.28 sham vs 153.7±22.19 leptin, ****P<0.0001, a.u.), and circularity (0.86±0.008 sham vs 0.87±0.02 leptin, *P<0.05, a.u.) compared to sham placentas and there was a trend for leptin to decrease mitochondrial area (0.11±0.008 sham vs 0.1±0.01 leptin, P=0.06, mcm) compared to the sham placentas. Overall, these data show that while leptin may not induce mitochondrial dysfunction in mouse placenta, leptin may increase mitochondrial fission, as shown by an increase in number and circularity. These markers of increased fission in the leptin treated placentas may indicate that there is disruption of the mitochondrial fusion/fission balance and may contribute to cardiovascular dysfunction and fetal growth restriction in preeclampsia.