The paper reports the outcome of a numerical simulation of turbulent flow over L-shaped riblets obtained by using a modified two-equation turbulence model. In the present paper, a modified version of the low-Reynolds-number k−ε model of Launder & Sharma (1974, LS hereafter) is introduced, in which the gradient production term of ε−equation is modeled to have only the normal derivative terms, and applied to the flows over the L-shaped riblets with finite thickness. And then systematical analysis is made on turbulence quantities. Compared to the original LS model, the present model has the drag reduction behavior and the flow field structure in better accord with both experimental results and the recent DNS results by Choi et al. (1993).