A diffusion theory model induced by a line source distribution is presented for oblique-incidence reflectometry. By fitting to this asymmetric diffusion model, the absorption and reduced scattering coefficients \mu_a and μ^'_s of the turbid medium can both be determined with accuracy of 10% from the absolute profile of the diffuse reflectance in the incident plane at the negative position –1.5 transport mean free path (mfp') away from the incident point; particularly, μ^'_s can be estimated from the data at positive positions within 0–1.0 mfp' with 10% accuracy. The method is verified by Monte Carlo simulations and experimentally tested on a phantom.