We investigated the electron and hole g-factors in individual InAs/GaAs quantum rings (QRs). From the magneto-photoluminescence measurements under a transverse magnetic field, we evaluated the in-plane g-factors of electron and hole spins by rotating the sample systematically around the crystal growth axis. The experimental results indicate that the in-plane and the out-of-plane anisotropies in hole g-factor are larger than those of electron g-factor, and the value of the hole in-plane g-factor varies largely from QR to QR while the electron g-factor is almost a constant value. From the model calculation considering the effects of shape anisotropies and uniaxial stress, we examined the correlation between the in-plane g-factors and the degree of valence band mixing. Further, the experimentally obtained trend in g-factors was in agreement qualitatively with theoretical consideration.