Background: Obstructive sleep apnea syndrome (OSAS) leads to right ventricular (RV) dysfunction and pulmonary hypertension (PH) in the later stages. Early determination of these conditions is very important. Objectives: We aimed to evaluate the correlations of pulmonary artery distensibility, right pulmonary artery fractional shortening (RPA-FS), and pulmonary artery stiffness (PAS) with PH among newly diagnosed OSAS patients. Methods: We prospectively evaluated 34 newly diagnosed OSAS patients and 28 controls. The study subgroups were determined according to the apnea-hypopnea index (AHI). All patients underwent a transthoracic echocardiographic examination. Conventional RV parameters, PAS, and RPA-FS parameters were measured. Results: RPA-FS was significantly lower in the OSAS group (p < 0.001) and positively correlated with tricuspid annular systolic excursion (TAPSE) (p = 0.047) and pulmonary acceleration time (PAT) (p = 0.006), and inversely correlated with systolic pulmonary artery pressure (sPAP) (p = 0.013), and PAS (p < 0.001). Consistent with this result, PAS was significantly worse in the patients with OSAS compared to the controls (27.1 ±3.5 to 15.8 ±2.7, p < 0.001), and inversely correlated with RPA-FS (p < 0.001), PAT (p = 0.001), and TAPSE (p = 0.035). PAS was positively correlated with sPAP (p = 0.001). There were statistically significant differences for both PAS and RPA-FS among the OSAS subgroups with regards to the severity of disease (p < 0.001). The correlation analyses showed a significantly positive correlation between RPA-FS and mean O2 saturation. RPA-FS was also inversely correlated with AHI. Similarly, PAS was positively correlated with AHI and arousal index. Conclusions: PAS and RPA-FS areworsened in patients with OSAS, and are correlated with PH and severity of OSAS.