A sero-surveillance study on hog cholera was conducted in the provinces of Nueva Ecija and Pampanga in the Philippines from June to November 2011 utilizing ELISA. Eight to nine samples of blood were gathered from each barangay making up 40-45 representative samples from each municipality and a total of 210 for the entire province. The absence of detectable levels of antibodies in the sera of pigs was the sole basis for evaluating the prevalence of hog cholera. Results of the study show that hog cholera was prevalent in pigs with and without a previous record of hog cholera vaccination. In the province of Nueva Ecija, the prevalence of hog cholera was 50.66% among vaccinated pigs and 31.67% in unvaccinated pigs. In Pampanga, hog cholera had a prevalence rate of 52.60% and 60.71% among vaccinated and unvaccinated pigs, respectively. Data demonstrated that unexpected vaccination failure and non-vaccination of pigs are the main factors that contribute to the prevalence of hog cholera in pigs raised under backyard conditions in the two provinces. This information will be necessary for many animal health practitioners whose advocacy is on the promotion of hog cholera control and prevention.