This paper proposes a widely tunable inductor realized by transmission lines (T- Line) for applications under 60 GHz. The inductor consists of several L-branch formed by short T-Line segments and variable distributed load capacitors. With changeable load capacitance, the equivalent inductance of whole T-Line would also be tunable. For conceptual demonstration, a prototype T-Line-C VCO is implemented for comparison to the conventional LC VCO. With the same ±50% capacitance variation rate, the traditional LC VCO with lumped inductors for comparison only achieves 11.6% frequency tuning range from 60.5 GHz to 67.6 GHz; However, the demonstrated VCO based on the proposed tunable T-Line inductors improve the frequency tuning range to 25.4% from 53.7 GHz to 68.4 GHz.