Human endogenous retroviral sequences family P (HERV-P) proviral sequences have been located within the human genome. Here, we identify and analyze novel putative structural genes of HERV-P in primates, human tissues, and cancer cells with an aim toward better understanding their evolutionary relationships and transcriptional potential. The expression pattern of HERV-P structural genes indicates that they are actively amplified in human tissues and widely expressed in cancer cells, suggesting a potential role in carcinogenesis. Phylogenetic analyses suggest that the HERV-P family may be divided into two distinct categories that arose during primate evolution via active gene duplication. Taken together, our data provide a better understanding of the dynamic evolutionary features and potential functional roles of the HERV-P gene family.