Background: According to the Indonesian Demographic and Health Survey (IDHS) in 2012 found that the main cause of maternal mortality in Jakarta is Hypertension (39%). Hypertension in pregnancy is caused by many factors, one of which is a low calcium diet. In the third semester of labor the need for calcium increases as the fetus begins to form and refine its bones, therefore the calcium level in the mother will reduce. This study was conducted to assess the association between a low calcium diet with hypertension in pregnant women. Method: This study used a cross-sectional design involving 161 pregnant women in the third trimester in Jakarta. Daily calcium data from the third-trimester mothers are taken by using the Food Frequency Questionnaire and interview, henceforth the blood pressure data is measured using a tensimeter. Data analysis using SPSS V.2.0 and the significance level used is 0.05. Result: Analysing using the Chi-square test, there was a significant relationship between a low calcium diet with hypertension in the pregnant woman. (P=0.000). Conclusion: This study shows a correlation between a low calcium diet with hypertension in pregnant women