Obsessive-Compulsive Disorder (OCD) is recognized as a severe and debilitating psychological illness. The purpose of the present study was to investigate the effectiveness of paradox therapy on patients with OCD. The present study recruited eighteen patients with OCD. Participants were assessed on the Yale Brown Obsessive-Compulsive Scale (YBOCS). Subsequently, they underwent six sessions of the PTC model of paradox therapy, each lasting approximately 45 minutes. A single group with pre- and post-assessment was adopted to evaluate the changes in the participants in response to the intervention. A linear mixed effect model with an unstructured residual covariance matrix was fitted to the data. A significant effect was evident for time, F (2, 17) = 108.8, p < .001. Direct comparison of mean scores showed a significant reduction from baseline to post-treatment; the mean difference = 20.22, SE = 1.5, p < .001, d = 2.1, and a significant but small reduction from post-treatment to follow-up, the mean difference = 1.56, SE = .41, p = .002, d = .16. The residuals were approximately normally distributed, skewness = .51, kurtosis = .7, and there were no extreme outliers. All participants showed a reliable change, i.e., a change more than expected from measurement error. Also, the improvement for all participants was clinically meaningful. The findings of the present study suggest that the PTC model of paradox therapy is efficacious in reducing the severity of obsessive-compulsive symptoms in patients with OCD.