The ruthenium complex catalyst system RuCl3-Pyridine-acetic acid-O-2, was found to be efficient to activate C-H bond of cyclohexane and O-2 in the oxidation of cyclohexane. The oxidation of cyclohexane conducted at 30degreesC and 1 atm pressure of O-2 gave cyclohexanone with traces of cyclohexanol. Formation of mu-oxo binuclear Ru-III complex was found to catalyze the oxidation of cyclohexane in which the rate of oxidation was found to increase on increasing the initial concentrations of catalyst and cyclohexane and partial pressure of O-2.