PURPOSE: To provide a method for selectively and efficiently detecting an acid-fast bacillus having proliferating property in fruit juice or fruit juice-containing acidic beverage and further having heat resistance, that is a thermotolerant acid-fast bacillus.

CONSTITUTION: The characteristic of this method for detecting thermotolerant acid-fast bacilli having proliferating property in an acidic fruit juice or an acidic beverage containing the acidic fruit juice comprises the following steps (A) to (C). (A) A sample of acidic fruit juice or an acidic beverage containing the acidic fruit juice is cultured in a culture medium for thermotolerant acid-fast bacilli to examine whether any bacterium grown in the culture medium exists or not, (B) When bacterium grown in the culture medium exists, whether or not ω-cyclohexane fatty acid in bacterial cell of the bacterium exists is examined. (C) When ω-cyclohexane fatty acid exists, the bacterium is judged to be the target thermotolerant acid-fast bacilli. By measuring ω-cyclohexane fatty acid using the above method, the existence of the thermotolerant acid-fast bacilli having proliferating property in the acidic fruit juice, etc., can be judged and sterilizing conditions are decided on control of microorganism or inspection in receiving fruit juice can efficiently be practiced.