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Anaerobic digestion of fish meal wastewater with high salinity and sodium (Na) content was investigated. The wastewater was collected from a fish meal factory. The chemical oxygen demand (COD) and pH of the wastewater were 8,530 mg/L and 6.58, respectively. The characteristics of wastewater were appropriate to be digested anaerobically except for the high salinity (13.03 ppt) and the Na content (7,986 mg/L). The wastewater was treated using single-stage and two-stage processing systems at room temperature (30 degrees C). The organic loading rates to the single-stage reactors were 0.28, 0.43, 0.85 and 1.71 kg COD/m(3)d. The organic loading rates to the two-stage reactors were approximately five times higher than those of the single-stage reactors. The results revealed that the percentage of methane (CH4) production from both types of operation was approximately 21%. For single-stage and two-stage operation, the COD degradation efficiency reached 75% and 69%, respectively; however, the maximum CH4 yield was 45 and 36 L, respectively, at STP/kg COD degraded, at an organic loading rate of 0.28 and 1.42 kg COD/m(3)d, respectively. An anaerobic process can be used for the treatment of organic wastewater with high salinity and Na content but not for CH4 production. The results indicated that high salinity and Na content adversely affected methane production.