A new measurement of the effective resonance integral of thorium metal has been made, using reactor oscillator techniques. Fluctuations in reactor power level, caused by oscillation of cadmium-shielded cylindrical samples, were recorded on a strip chart. The signal was Fourier-analyzed, and the coefficient of the fundamental mode determined. For a constant shape reactivity input, the value of this coefficient for each sample is proportional to the effective resonance integral of the sample. The scattering effects of the thorium were determined by oscillating identical samples of lead, and were deducted from the results for the thorium. Absolute calibration of the oscillator measurements was provided by oscillating several dilute solutions of each of three standard absorbers : boron, indium, and gold. The effective resonance integrals of the thorium cylinders were then found to be given by the formula: where S/M is the surface-to-mass ratio of the samples in cm2/gm. The 1/v component of the resonance integral, 3.6 barns, has been removed from the first term of this formula.