Immunization has been recommended for reducing infant morbidity due to communicable diseases like tetanus, diphtheria, whooping cough, poliomyelitis, measles, tuberculosis, hepatitis and yellow fever. This study investigated the knowledge, beliefs, and practices (KBP) of nursing mothers concerning utilization of immunization in Ogun State, Southwest Nigeria. Structured pretested questionnaire was used to collect data from 120 nursing mothers of under 5 children. Data gathered were analyzed using descriptive statistics. The findings of the study revealed that 51% of mothers have at least secondary school education, 60% were of the Yoruba tribe and 65% were Christians. As a result of mothersâ€™ KBP, 51% had children with incomplete immunization status. Respondentsâ€™ had inadequate knowledge especially regarding the number times vaccines must be administered to their infants even though 93% believe that childhood immunization is generally a good initiative. The risk of not having their child adequately immunized and on schedule eludes majority of the respondents, thus, the study recommends that health education campaign highlighting importance of complete schedule of childhood immunization should target nursing mothers to improve the child health status.