The influence of the hole length-to-diameter ratio on the film-cooling performance is numerically investigated for the cylindrical hole and laidback fan-shaped hole with an inlet groove. Numerical analysis of film-cooling effectiveness is carried out by solving three-dimensional Reynolds averaged Navier-Stokes equations (RANS) with a realizable k-ε turbulence model. Rectangular and triangular grooves are applied to the inlet of the film-cooling hole, and the ratio of the hole length (L) to the diameter (D), i.e., L/D, is varied with L/D = 6 ~ 12 at blowing ratios of 0.5 to 1.5 for cylindrical hole and 0.5 to 3.0 for laidback fan-shaped hole. For cylindrical holes with an inlet groove, the film cooling effectiveness decreases as the hole length increases, regardless of the blowing ratio. However, in the case of laidback fan-shaped holes, the cooling performance for length-to diameter ratios show different tendency for each blowing ratio. At a low blowing ratio (M = 1.0), a relatively high effectiveness is observed at relatively long lengths (L/D = 10, 12). On the other hand, the performance has the maximum at L/D = 8 under high blowing ratio conditions (M = 3.0).