Oyster production is a recent and expanding practice in the Brazilian coast. The mangrove oyster Crassostrea gasar is mainly produced in the northeastern (NE) region. Since 2008, the protozoan parasite Perkinsus spp. has been detected in oysters from several states of the Brazilian coast, reaching a high prevalence, representing a sanitary issue for the future. In the present project, we used a transcriptomic approach by performing RNA-seq of hemocytes of C. gasar oysters from a culture area in the Mamanguape estuary (Paraiba State, NE). First, Perkinsus spp. (P. beihaiensis and P. marinus) were diagnosed, and heavily infected and uninfected oysters were selected to prepare hemocyte pools for further RNA extraction, cDNA library construction, and sequencing.