Third trimester pregnant women were most likely to experience complaints such as frequent urination, constipation, difficulty sleeping, back pain. Back pain was pain that occured in the lumbosacral area (backbone). Back pain intensity would increase with advancing gestational age because this pain was the result of a shift in the woman's center of gravity and her posture. This study aimed to determine the description of low back pain in third trimester pregnant women. The design of this research was descriptive. The population in this study was all third trimester pregnant women who experienced low back pain at the Puspo Public Health Center, Pasuruan Regency in August 2021, as many as 32 people. The sampling technique of this research was total sampling. The sample in this study as many as 32 people. The research instrument used Numeric Rating Scale pain checklist. Data analysis used frequency distribution and percentage. The results suggeted that back pain experienced by pregnant women in the third trimester, most of the respondents experienced moderate pain, as many as 22 people (68.8%), mild pain was 9 people (28.1%), and severe pain was 1 person (3, 1%). Data analysis suggested that most of the respondents experienced moderate pain. Back pain was caused by estrogen and progesterone hormones which relaxed the joints, bones and muscles in the hips. As the baby grew, the curvature in the lumbar spine could increase as the abdomen was pushed forward, this could also cause back pain