The influence of anisotropic thermal diffusivities on non-destructive testing of CFRP laminates using pulse phase thermography (PPT) was studied analytically. The results show that the optimum frequency for maximizing detectable depths of defects increases concomitantly with the increase in the ratio of the thermal diffusivities in the through-thickness direction to that in the in-plane direction (alpha'). Furthermore, the phase difference between sound and defective areas decreases significantly with decreased alpha'. These predicted tendencies were verified through experiments. Experimental results also demonstrated that defects of 10 mm in diameter can be detected up to around 5 mm depth in CFRP with lower alpha', but only to around 1 mm in CFRP with higher alpha'.