<p>As a key economic marine aquaculture species in China, sea cucumbers (<i>Apostichopus japonicus</i>) were widely cultured in coastal regions, where were susceptible to crude oil pollution threatening their survival and population recruitment, and the impact of crude oil on non-specific immune functions of sea cucumbers was still limited. Therefore, this study exposed sea cucumbers to water-accommodated fractions (WAFs) of Oman crude oil for 7 d to investigate the effects of crude oil on non-specific immune functions, which were composed of cellular and humoral immune responses. Results showed that WAFs exposure caused oxidative stress and lipid peroxidation, evidenced by elevated reactive oxygen species levels in coelomocytes and initially increased and then reduced malondialdehyde content in coelomic fluid of sea cucumbers. For cellular immune, results showed that WAFs exposure caused dysregulation of phagocytic activity, and a rough reduction in total cell count and an obvious increase in respiratory burst capacity in coelomocytes in a dose-dependent manner, indicating coelomocytes dysfunction and suppression of cellular immune function. Regarding humoral immune function, an obvious decrease in the lysozyme content, total nitric oxide synthase, acid phosphatase and alkaline phosphatase activities, was observed in coelomic fluid with the increase in total petroleum hydrocarbons concentrations, indicating lysosomal dysfunction and suppression of humoral immune function. These findings revealed adverse effects on both cellular and humoral immune responses, suggesting acute immunotoxicity of crude oil in sea cucumbers.</p>