This experiment was conducted to study the tolerance dose of hybrid sturgeon (Acipenser ruthenus ♂ × A. baeri ♀) to montmorillonite as a mycotoxin adsorbent in diets. Five experimental diets were formulated with 0 (control), 0.5%, 1.0%, 2.5% and 5.0% wheat middlings replacement by the equal level of montmorillonite (domestic, feed-grade and modified montmorillonite, the fineness≥99%) in a basal diet, and the aflatoxin B₁ content in the basal diet was <10.00 μg/kg. Six hundred hybrid sturgeon with an initial average body weight of (45.10±0.12) g were randomly assigned to 5 groups with 6 replicates per group and 20 hybrid sturgeon per replicate. Each group was fed one of five diets. After 70 days, the growth performance, body composition, blood physiological and biochemical indexes and the tissue changes of intestine and liver were tested to determine the tolerance dose of montmorillonite for hybrid sturgeon. The results showed that final body weight (FBW) and specific gain rate (SGR) of fish fed the diets with 0.5% and 2.5% montmorillonite were significantly decreased (P<0.05), and hepatosomatic index (HSI) of fish fed the diet with 5.0% montmorillonite was significantly increased (P<0.05), while there were no significant effects on the growth performance indexes between 1.0% group and control group (P>0.05). Plasma aspartate aminotransferase (AST) activity was gradually increased with the montmorillonite supplemental level increasing, and that in 1.0%, 2.5% and 5.0% groups was significantly higher than that in control group, but there was no significant difference between 0.5% group and control group (P>0.05). With the montmorillonite supplemental level increasing, plasma AST/alanine transarninase (ALT) kept on rising which rose to 2.00 from 1.09. Whole blood respiratory burst (RB) level in 1.0% group was the highest, and was significantly higher than that in other groups (P<0.05). Plasma malondialdehyde (MDA) content in 1.0% and 5.0% groups was significantly higher than that in control group and 2.5% group (P<0.05), and was little higher than that in 0.5% group (P>0.05). Tissue sections of intestine and liver showed that significant negative effects on intestine and liver tissues were found when montmorillonite supplemental level was ≥2.5%. Based on a comprehensive consideration of all indexes, we suggest that the tested montmorillonite as a mycotoxin adsorbent supplement into the hybrid sturgeon diet should be more than 0.5% and less than 2.5%, that is, the tolerance dose of the tested montmorillonite for hybrid sturgeon is between 0.5% and 2.5%.