Most vaccine are very safe, however, similar to drug, vaccine can cause adverse even after immunization at difference levels. Those adverse even can prevent or minimize with the close cooperation between health workers and mothers. The authors conduct this descriptive study focus on the practice of mother on monitoring children after immunization in Ha Long, Quang Ninh in 2011. Information collected by observing and interview mother in health center right after their children have immunization and at their house after three days by investigation form. The results have shown that 11.4 percent of mothers did not provide their children health situation to health worker before immunization. 13.5 percent of mothers did not monitor their child after immunization in health center. 8.6 percent of mother not meet the minimum time of monitoring their child at home. The reason that mother not follow the guideline of child monitoring include: 43.8 percent don't know
40.2 percent known but too busy, 18.8 percent think that is not necessary. Health-worker's consultation and guiding to mother before immunization is important to help mothers understand and selfawareness on monitoring their children, which help better care for children and increase the immunization safety.