Hepatitis B virus remains a major public health problem around the world, especially in developing countries in Asia prevalence more than 8%. In Thailand, there are thousands of children under the age of 5 years have HBV infected from mother to child transmission. Infants infected with HBV from their mothers are at risk of developing hepatocellular carcinoma and hepatic cancer at 90%. Since 2017, Thai national guidelines have recommended that mothers with high viral load or HBeAg positivity use Tenofovir Disoproxil Fumarate (TDF) to prevent HBV transmission from mother to child. This study armed to evaluate of the transmission rate and factors associated with Mother to Child Transmission (MTCT). The retrospective cohort studies analysis was conducted using the transmission of hepatitis B from mother to child data. Records of 342 pregnancy woman who hepatitis B infection were obtained. Participants mother at study entry must be Hepatitis B Surface Antigen (HBsAg) positive from 2018 to 2020 were reviewed. Details of the mother factors such as Underlying disease, Fertility planning, ANC visit, HBeAg status, viral load level and mode of delivery and Infant factors such as body weight, active- passive immunoglobulin, breast milk status included TDF used for mother HBV prevention data. Transmission rate was calculated and risk factors for MTCT were assessed using a multivariable binary regression model. There were 42.40% (145) infants born from mothers received TDF and 57.60% (197) infants born to non TDF-used mothers. 52.92% were uninformed that they had hepatitis B, and more than half (52.34%) were diagnosed as hepatitis B positive during their pregnancies. All 342 infants received hepatitis B vaccine at birth, 323 infants received Hepatitis B Immune Globulin (HBIG) and hepatitis B vaccine and 5.56% (19) who did not received Hepatitis B Immune Globulin (HBIG). The overall MTCT incidence rate is 0.88%, the MTCT rate among TDF mothers is 0.69%, and the MTCT rate among non-TDF mothers is 1.02%. However no association between risk factor and MTCT among mothers HBsAg positive.