The purpose of this study was to ana1yze the joint stiffness after immobi1ization in a rat's lower extremity model. Rat knee joints were surgically immobilized in a full flexed position for periods of up to 7 weeks with or without intraarticular intervention. The biomechanical analysis was assessed by measuring the bone-joint-bone sample as a cantilever. Measurement was performed with (a) knee flexion angle with gravity, (b) fast Fourier transform analysis of time-dependent mechanical noise with random frequencies, and (c) dynamic stiffness and loss tangent with sinusoidal vibration at a certain frequency. The results showed that the conventional static mechanical test could not detect the intraarticular changes of the whole knee joint. The measurement of the viscoelastic properties covering wide frequencies revealed that an accurate change occurred.