Transmission of bloodborne pathogens by means of unsafe injection practices is a significant public health problem in developing countries. Although the overall proportion for immunization is low among injections, unsafe immunization practices affect mostly infants, a population with an increased likelihood of becoming hepatitis B virus carriers. This study estimated the prevalence of unsafe injection among vaccinators working at the peripheral level in northwestern China and the risk of HBV infections among infant vaccinees, and analyzed factors contributing to the most prevalent unsafe practice: the reuse of a non-sterilized reusable syringe among infants. A knowledge-attitude-practice survey was conducted in which 180 peripheral vaccinators selected by multi-stage cluster sampling in each of four provinces and one autonomous region completed a self-administered questionnaire. The lack of observational data for assessing the validity of the self-reported practices made the study prone to systematic respondent bias that may have skewed the results towards underestimation of unsafe practices. The minimum estimate of the percentage of peripheral vaccinators reusing a syringe and/or needle without sterilization between infants was 7.2-55.0%, whereas the percentage of those disposing of used disposable syringes and needles inappropriately was 8.9-23.3% by province. According to a model-based estimate, the annual number of HBV infections among 100,000 fully immunized children due to unsafe immunization injection was at least 135-3120. An insufficient supply of syringes and the attitude to justify reuse were significantly associated with the unsafe reuse of a reusable syringe in most part of the area studied. Introduction of auto-disable syringes may contribute to curb the unsafe practices, but the development of safe collection and disposal procedures for used syringes and needles is prerequisite. Sufficient supply of equipment as well as training, supervision, and monitoring targeting specifically on the risk behaviors and concerned attitudes are essential for behavior changes among the vaccinators.