Objective To explore the effect of plasma glucose management on placental ultrastructure in pregnant women with gestational diabetes mellitus, so as to provide scientific evidence for optimizing the management during pregnancy. Methods Pregnant women with gestational diabetes mellitus were divided into satisfied glucose control group and dissatisfied glucose control group; meanwhile, normal pregnant women were taken as controls. All the participants received antenatal care until delivery in the First People's Hospital of Nantong from January 2013 to December 2014. Plasma glucose levels of the three groups were examined and the placental ultrastructure was observed by transmission electron microscopy. Results (1) Finally 57 pregnant women were included in this study. There were 32 pregnant women with gestational diabetes mellitus (56.14%, 32/57) and 25 with normal glucose (43.86%, 25/57). The proportions of pregnant women with satisfied and dissatisfied glucose control were 35.09% (20/57) and 21.05% (12/57), respectively. (2) There were no significant differences in the age, gestational weeks of oral glucose tolerance test (OGTT), gestational weeks of labor, blood pressure or body mass index between the three groups (P>0.05). (3) After plasma glucose management, there was no significant difference in fasting blood glucose between the three groups (P=0.099). And no significant differences were found in 2 h postprandial blood glucose, nocturnal blood glucose, or glycosylated hemoglobin between satisfied glucose control group and healthy control group (P>0.05). The 2 h postprandial blood glucose, nocturnal blood glucose and glycosylated hemoglobin in the dissatisfied glucose control group were significantly higher than those in the other two groups (P<0.01). (4) There was no significant difference in the placental ultrastructure changes between the satisfied glucose control group and control group (P>0.05). The proportions of participants with placental ultrastructure changes in the dissatisfied glucose control group were significantly different from those of the other two groups (P<0.01). Conclusion Hyperglycemia is a risk factor for placental ultrastructure change in pregnant women with gestational diabetes mellitus; the management of plasma glucose should be strengthened during pregnancy, so as to avoid the placental ultrastructure change and to reduce adverse pregnancy.