In order to investigate the effect of disturbance due to sampling upon the undrained strength of clay, several repeated triaxial compression tests up to failure were carried out. The decrease in the residual effective stress due to disturbance results in a similar effect on the strength behavior to that due to rebound, and the repeated compression test gives an easy method to obtain accurately the Hvorslev's strength parameters with few specimens. The strength ratio of the disturbed sample to the perfect one has a unique relation with the residual effective stress ratio of the latter to the former. regardless the kind of disturbance, and the repeated loading test suggests a most simple and practical method for correcting the undrained strength of a disturbed sample.