In order to assess the effect of dietary arachidonic acid on the immune-related genes expression and Vibrio-resistance in white shrimp Litopenaeus vannamei, two series of isonitrogenous and isoenergetic experimental diets based on either fish oil or blended vegetable oil, both with the equivalents of saturated fatty acids(SFA), mono-unsaturated fatty acids (MUFA), poly-unsaturated fatty acids (PUFA), and n-3/n-6 ratios, were fed to the white shrimp respectively for six weeks. Then the mRNA expression levels of Toll receptor, IMD and lysozyme in gills of all shrimp before and after Vibrio alginolyticus challenge(24, 36 and 42 h), and Vibrio-resistance of all the shrimp were investigated.The results showed that: ① The mRNA expressions of Toll receptor, IMD and lysozyme in gills of the shrimp fed diets based on fish oil (containing 5.85 mg DHA/g diet and 3.83 EPA mg/g diet), first increased, then decreased along with the increasing dietary ARA level. Compared to the other treatments, the shrimp in treatments of 0.56 mg ARA/g diet (B group) and 0.87mg ARA/g diet (C group)displayed significant higher lysozyme mRNA expression levels(P < 0.05). The mRNA expressions of Toll receptor, IMD and lysozyme in gills of the shrimp fed diets based on vegetable oil (containing 3.28 mg DHA/g diet and 1.87 mg EPA/g diet), increased along with the dietary ARA level. The Toll receptor mRNA expression level in treatment I(1.44 mg ARA/g diet) was significantly higher than F group(0.19 mg ARA/g diet)(P < 0.05). ② The mRNA expressions of Toll receptor, IMD and lysozyme in gills of all shrimp changed significantly when the shrimp experienced Vibrio challenge. For the shrimp fed diets based on fish oil, the peak of mRNA expressions of Toll receptor, IMD and lysozyme appeared at 24, 42 and 24 h respectively. The maximum expressions of all the three genes appeared in B treatment(0.56 mgARA/g diet). For the shrimp fed diets based on vegetable oil, the peak of mRNA expressions of Toll receptor, IMD and lysozyme appeared at 24, 42 and 36 h respectively. For the shrimp fed diets based on vegetable oil,the maximum expressions of all the three genes appeared in I treatment (1.44 mg ARA/g diet). ③ There was no significant difference in cumulative mortality among the different ARA treatments when the shrimp were challenged with V. alginolyticus for 96 h. It is therefore suggested that dietary ARA level could regulate the expressions of these immune-related genes of the white shrimp, and ARA's regulation on immune related genes could be affected by dietary DHA and EPA levels.