Psidium guajava L. is known to possess immune-modulatory properties in humans and other mammals. Although the positive effects of P. guajava-based diets on the immunological status have been shown for some fish species, the underlying molecular mechanisms of its protective effects remain to be investigated. The aims of this study were to evaluate the immune-modulatory effects of two guava fractions from dichloromethane (CC) and ethyl acetate (EA) on striped catfish with in vitro and in vivo experiments. Striped catfish head kidney leukocytes were stimulated with 40, 20, 10 and 0 μg/ml of each extract fraction, and the immune parameters (ROS, NOS, and lysozyme) were examined at 6 and 24 h post stimulation. A final concentration of each fraction at 40, 10 and 0 μg/fish was then intraperitoneally injected into the fish. After 6, 24, and 72 h of administration, immune parameters as well as the expression of some cytokines related to innate and adaptive immune responses, inflammation, and apoptosis were measured in the head kidney. Results indicated that the humoral (lysozyme) and cellular (ROS and NOS) immune endpoints were regulated differently by CC and EA fractions depending on dose and time in both, in vitro and in vivo experiments. With regards to the in vivo experiment, the CC fraction of the guava extract could significantly enhance the TLRs-MyD88-NF-κB signaling pathway by upregulating its cytokine genes (tlr1, tlr4, myd88, and traf6), following the upregulation of inflammatory (nfκb, tnf, il1β, and il6) and apoptosis (tp53 and casp8) genes 6 h after injection. Moreover, fish treated with both CC and EA fractions significantly enhanced cytokine gene expression including lys and inos at the later time points - 24 h or 72 h. Our observations suggest that P. guajava fractions modulate the immune, inflammatory, and apoptotic pathways