Background/Aim: Obstructive sleep apnea syndrome (OSAS) is associated with intermittent episodes of hypoxia, endothelial dysfunction and associated cardiovascular problems. Our aim was to investigate whether OSAS-related hypoxia alters the expression of rhoassociated protein kinase (ROCK), a marker of chronic hypoxia and endothelial dysfunction. Materials and Methods: ROCK1 and ROCK2 levels were measured by immunoblotting in peripheral blood mononuclear cells (PBMC) of 47 OSAS patients and 17 healthy controls. Results: OSAS patients showed significantly lower PBMC ROCK1 and ROCK2 levels than healthy controls in the morning, but not in the evening. ROCK1/2 levels were correlated with blood triglyceride, visceral adiposity index, minimum oxygen saturation, C-reactive protein concentration, lymphocyte levels and sleep efficiency. Conclusion: Intermittent hypoxia induced by OSAS does not permanently alter ROCK protein expression levels. OSAS appears to be associated with endothelial dysfunction through inflammation and lipid metabolism pathways.