Pregnancy is a great stressful physiological condition in women during their reproductive period. During pregnancy several hemodynamic, biochemical and hematological modifications occur as a part of the physiological adaptation of the body. Changes in blood pressure occur in third trimester of pregnancy, which may be associated with increased maternal and infant mortality and morbidity. This cross-sectional study was carried out in the Department of Physiology, Mymensingh Medical College, Mymensingh, from July 2013 to June 2014. Study subjects were selected by following purposive sampling procedure and the protocol of this study was approved by Institutional Ethics Committee (IEC) of Mymensingh. This study enrolled 100 pregnant women of third trimester of pregnancy and 100 aged matched non-pregnant women from Mymensingh district. Mean systolic blood pressure in study group were 124.8±14.51 mm of Hg and in control group were 106.50±10.67 mm of Hg, which was statistically increased. Diastolic blood pressure in study group was 83.00±13.37 mm of Hg and in control group 71.05±7.12 mm of Hg, which was also statistically significant. The changes in blood pressure in third trimester of pregnancy is the major concern of developing the risk of pre-eclampsia & eclampsia, and increased prevalence of IUGR, pre-maturity and perinatal mortality. This study reveals significant changes of blood pressure during third trimester of pregnancy.