Thermal diffusivity measurements are carried out in certain organic liquids using the pulsed dual beam thermal lens technique. The 532 nm pulses from a frequency doubled Q-switchedNd:YAG laser are used as the heating source and an intensity stabilized He-Ne laser serves as the probe beam. Experimental determination of the characteristic time constant of the transient thermal lens signal is verified theoretically. Measured thermal diffusivity values are in excellent agreement with literature values. © 1998 Society of Photo-Optical Instrumentation Engineers.