We examine the impact of state-owned shareholders on fraud within private firms. Utilizing a sample of A-share private listed firms in China observed from 2008 to 2021. We discover a significant negative association between state-owned shareholders and the likelihood of fraud in private firms. State-owned shareholders primarily act as inhibitors of fraud, and their effect on the probability of fraud being detected is not statistically significant. This finding remains robust even after conducting a series of sensitivity tests to mitigate potential selectivity bias and reverse causality endogeneity issues. In the analysis of heterogeneity, we found that state-owned shareholders play a more active role under conditions of imperfect external institutional development, and they also exert a more significant inhibitory effect on enterprises with lower governance levels and higher business risks. Our mechanism test demonstrates that the inhibitory effect of state-owned shareholders on corporate fraud is achieved by improving corporate governance and alleviating financial distress. This study also examines the impact of state-owned shareholders' local characteristics, external supervision mechanisms, and internal governance mechanisms in unique Chinese enterprises on fraudulent behaviour by private enterprises. Overall, our study provides empirical evidence that state-owned shareholder ownership is associated with reducing fraudulent behaviour within private firms.