Abstract： Background Recent research suggested that obstructive sleep apnea syndrome (OSAS) might be independently associated with hypoadiponectinemia, which was linked to some complications of OSAS, such as hypertension, diabetes,etc. This study was conducted to investigate the effect of continuous positive airway pressure (CPAP) treatment on changes of both serum adiponectin levels and mean arterial pressure and their possible links in male OSAS patients.Methods Twenty-three adult male patients with moderate-to-severe OSAS but without obesity, coronary heart disease and diabetes were recruited. Their blood sampleswere collected and moming mean arterial pressure (MAP) was measured before CPAP treatment and on day 3, 7, 14 of CPAP treatment respectively. The serum adiponectin concentration was tested with radioimmunoassay.Results Compared with the serum adiponectin level before CPAP treatment, no significant change was found in OSAS patients on day 3 and day 7 of CPAP treatment (P＞0.05). It was not until day 14 of CPAP treatment did a significant elevation in serum adiponectin level occur (P＜0.01). Meanwhile, the MAP showed no statistically significant difference among its levels before CPAP, on day 3 and day 7 of CPAP treatment (P＞0.05). However, on day 14 of CPAP treatment,a significantly lower MAP than that obtained before treatment was observed (P＜0.05).Conclusions CPAP treatment can gradually reverse hypoadiponectinemia and reduce MAP in OSAS patients.Hypoadiponectinemia might be involved in the pathogenesis of OSAS-mediated hypertension.