Tantalum oxide (Ta<sub>x</sub>O<sub>y</sub>) as high refractive index material has been grown on p-type silicon and quartz substrates by R.F. magnetron sputtering with our innovative technique called “reactive-gas timing”. The reactive gas timing technique is an on-off time period sequence between argon (Ar) and oxygen (O<sub>2</sub>) plasma during sputtering process. The technique of gas-timing plays the effect on the properties of Ta<sub>x</sub>O<sub>y</sub> thin film. The bombarded Ar-plasma was varied at 2, 5 and 8 sec, while the period of reactive O<sub>2</sub>-plasma was kept at 5 sec in this experiment. The physical and optical properties were investigated by using X-ray diffraction (XRD), Atomic Force Microscope (AMF), UV-Visible spectrometer and Spectroscopic Ellipsometer, respectively. The XRD spectra and AFM photographs show all films are amorphous phase with smooth feature. Meanwhile the transmittance of sputtered thin film decreases with 10% and the absorption edge shifts to lower energy with the increasing of the argon period from 2 sec to 8 sec. The refractive index as showed by ellipsometry slightly increases from 2.08 to 2.17 at wavelength 550 nm with the increasing of argon period from 2 sec to 8 sec. The increasing of the refractive index might dues to tantalum (Ta) rich which consists in thin films. The Ar-plasma period in the deposited film plays an important role on the properties of the Ta<sub>x</sub>O<sub>y</sub> thin films especially as optical refractive index material.