Abstract: The present invention relates to a method for detecting a nucleic acid of a gut microorganism in a sample using a nucleic acid of a bacterium as an internal control nucleic acid selected from a normal gut flora, and to a composition for nucleic acid amplification used in the method. The internal control according to the present invention is present in the sample from the beginning, and thus there is no inconvenience of separately adding an internal control after the sample collection process, and may be used as an internal control for the sample collection process, an internal control for the nucleic acid extraction process, and an internal control for the nucleic acid amplification process. In addition, the presence or absence of the nucleic acid of the gut microorganism in the sample may be detected with a high accuracy through the minimization of false negative and false-positive determinations by using the nucleic acid of the bacterium as the internal control selected from the normal gut flora.