A new linear inverse method is demonstrated for recovery of particle-size distribution (PSD) and volume fraction of opaque colloidal suspensions from frequency domain photon migration (FDPM) measurement of multiply scattered light. To deal with the ill posedness of PSD retrieving problem, the size distribution is approximated by the B-spline expansion. Tikhonov regularization, along with both nonnegativity and smoothing constraints, in which the L-curve method is employed to choose a regularization parameter, are also used to ensure the stable and realistic solution. The algorithm is tested using synthetic FDPM measurements at a variety of size distributions, and results are compared using other inverse methods. The influences of model and measurement error are investigated. To demonstrate our inversion approach, PSD and volume fraction of opaque titanium dioxide suspensions are recovered from actual FDPM measurements. This work demonstrates the ability of FDPM method to characterize colloidal suspensions.