To investigate the effects of carvacrol supplementation in rainbow trout induced by lipopolysaccharide (LPS), relative gene expressions levels of some pro-inflammatory cytokines and apoptosis markers in kidney and liver were measured. Fish with a mean weight of 44.71±1.33 g were studied using four different treatments with three replicates each. Inflammation and apoptosis were performed using LPS of Escherichia coli (25 µg ml ^-1) except in the control group and only carvacrol (100 µg ml ^-1 diet) containing diets were fed to this group (CAR). The last group was the infected fish fed carvacrol supplemented diet (+CAR). Kidney and liver tissues were removed 3 days after to determine the levels of interleukin-1β (IL-1β), interferon gamma (INF-γ), caspase 3 (Cas 3), caspase 8 (Cas 8) using Real-Time PCR analyses. IL-1β expressions of both kidney and liver was significantly decreased (12.9 and 2.14 fold, respectively) in LPS treated cells (p〈0.05). While IFN-γ expression was up regulated in kidney, it had down regulation in liver. LPS decreased both Cas 3 and 8 expressions in kidney but increased in liver. +CAR increased expressions of IL-1β and IFN-γ compared with the control (up to 2-3 fold) in all tissues except caspase gene expressions that were similar in the control. In all tissues, IL-1β and IFN-γ expressions increased in +CAR group, expect IFN-γ in the kidney. However, Cas 3 and 8 expressions including apoptosis was induced by up-down regulations in all tissues compared to LPS-injected fish. The results showed that carvacrol had pro-inflammatory and apoptotic effects especially on liver tissue of LPS-induced inflammation model of Oncorhynchus mykiss.