Hepatitis B virus (HBV) infection is highly prevalent in Mongolia and its sequelae including liver cirrhosis and liver cancer are crucial public health problems in Mongolia. HBV infection is preventable through the vaccination. Universal hepatitis B vaccination has been introduced in 1991 after the 3 years field trial, making our country the 20th country with obligatory immunization against hepaitis B of all eligible population. In addition a penta vaccine (DTP+HipB+HBV) was introduced since 2005 in urban and rural areas. Although statistical information is available regarding the coverage of these hepatitis B vaccines, no study has been conducted on the coverage of hepatitis B vaccination based on the immunization cards of children that is important to reveal the current situation in the country. Objective: To study the coverage of Hepatitis B vaccination among children born after more than 10 years since its implementation in Mongolia. Materials and Methods: Nationwide cross-sectional survey was conducted during 2009-2010. A total of 5894 children was enrolled in this survey selected from Ulaanbaatar, Darkhan, Erdenet as well as 11 provinces and 50 soums. Iimmunization data of each child was abstracted from the health records or immunization cards at the actual Health Center, Local or Family hospital. The hepatitis B vaccination coverage was assessed by measuring HepB-birth dose, second and third dose. The vaccination status of the child was determined by counting the immunizations that were recorded by health/immunization registry or card. Data analyses was performed using SPSS 17.0 software. Results: A total of 5894 children were participated in the survey out of 6380 selected children (response rate 92.38%). Vaccination cards or registrations were available for 4944 (83.9%) children that was higher in rural areas compared to cities (Ulaanbaatar, Darkhan, Erdenet 75.5%, province centers 87.3%, soums 90.5%, p<0.001). In addition, the proportion of children with vaccination card was significantly decreased by age from age of 4 years to 6 years (p<0.0001). Vaccination coverage rate of those who received at least one dose of hepatitis B or penta vaccine was 98.6% [(95% confidence interval: 98.36-98.98) and 81.9% of them were fully vaccinated whereas 16.7% were partially vaccinated. Vaccination rate was 97.8% in Ulaanbaatar, Darkhan and Erdenet cities, 99.2% in province centers and 99.1% in rural soums. According to the results of 11 provinces and, coverage rate in provinces was 98.3%-100% where Umnugovi and Khentii provinces had highest rate (100%) and Selenge and Zavkhan provinces had lower rates (98.7%). Around 95% of the children were received the first dose of hepatitis B vaccine, of whom 3413 (76.5%) received within 24 hours while 1274 (27.8%) had received later than the schedule. Among study population 13.1% were vaccinated with penta vaccine that was introduced in 1995 in Mongolia. Conclusion: 1. Vaccination cards were available for 4944 (83.9%) children that was significantly higher in rural areas compared to cities. 2. Vaccination coverage rate of those who received at least one dose of hepatitis B or penta vaccine was 98.6% [(95% confidence interval: 98.36-98.98) and 81.9% of them were fully vaccinated whereas 16.7% were partially vaccinated. 3. Around 95% of the children were received the first dose of hepatitis B vaccine, of whom 3413 (72.8%) received within 24 hours while 1274 (27.8%) had received later than the schedule.