This paper reports on the design and fabrication of Poly(dimethylsiloxane) (PDMS) single mode rib waveguide. PDMS was chosen as the base material for both the core and cladding of the waveguide. Such a PDMS waveguide allows an easy integration with microoptical components for lab-on-a-chip systems fabricated by soft lithography fabrication methods. The modification of the PDMS refractive index was achieved by diluting the base material with hexane. The fabricated PDMS rib waveguides were characterized for mode profile characteristics and the results confirmed the excitation of the waveguide's fundamental mode. The propagation loss was characterized at a wavelength of 635 nm and found to be 0.48 dB/cm. Such a low loss waveguide is useful as basic building block for complex microphonotnics device.