Background: Pulmonary hypertension is a condition which there is an increase in mean pulmonary artery pressure measured at ≥25 mmHg. The gold standard in diagnosing this condition is right heart catheterization. Enlargement of right descending pulmonary artery on chest radiographs is a sign of pulmonary hypertension. However, the value of radiographic measurements reported was diverse. The study analyzes the correlation between the right descending pulmonary artery (RDPA) diameter on chest radiographs and means pulmonary artery pressure on right heart catheterization to understand whether RDPA diameter on chest X-ray could be a predictor in determining the severity of pulmonary hypertension.Methods: Thirty-five subjects were reviewed to compare RDPA diameter from a chest X-ray on posteroanterior projection and mPAP value from the right heart catheterization. The correlation between them was analyzed using Pearson's correlation test.  RDPA diameter cut-off point was defined using the ROC curve.Result: RDPA diameter and mPAP revealed a high positive correlation (p<0.001; r=0.824). The cut-off value of the RDPA diameter was 21.8 mm (sensitivity 81% and specificity 85.7%; AUC =0.9)Conclusion: The measurement of right descending pulmonary artery diameter on chest x-ray positively correlates with mean pulmonary artery pressure. Therefore, the diameter of the right pulmonary artery on the chest x-ray can predict the severity of pulmonary hypertension.