Background: Malaria and hepatitis B virus (HBV) are two diseases of major medical importance in Nigeria. Methods: The study determined the preponderance of malaria, HBV and their co-infection among 600 outpatients of three major hospitals in Port Harcourt, Nigeria, using standard microscopic method and rapid serology assay diagnostic kit. Results: Total preponderance rate of malaria, HBV, and co-infection was observed to be 41.0%, 6.0%, and 4.33%, respectively. The female gender was more infected with malaria (44.67%) than the male counterparts (37.54%), while the males were more infected with HBV (7.12%) and co-infection (5.18%) than the females with 4.8% and 3.44%, respectively. The infection rate between genders was not statistically significant (P > 0.05). The prevalence of malaria was statistically high among the age group of 21-30 years (55.66%) (P < 0.05). HBV and co-infection prevalence rate was statistically the highest among the age group of 21-30 years with 11.76% and 10.3% rates of infection, respectively. Conclusions: The high rate of malaria prevalence and the presence of HBV and co-infection among the study subjects imply that these infections are threats to the human health and strategies should be adopted to help combat and control these infections.