We have investigated the guided optical properties of a Ti:LiNbO$_3$optical waveguide which was fabricated by Ti-diffusion in an air atmosphere and proposed an effective polishing method of waveguide endfaces. And the results of guided optical mode and fabrication condition were obtained as follows; circled1 propagation loss : 0.53 dB/cm circled2 mode size : horizontal/vertical=12.5${mu}{ extrm}{m}$ circled3 mode mismatch : 1.7 dB circled4 diffusion temperature : 105$0^{circ}C$, time : 8 hours circled5 atmosphere : air