Abstract: Based on proposing a new equation B=Bo + B_I In (t+1) +B₁₁ 1n² (t + 1) for fitting the relaxation curve, a new relaxation parameter, which can characterize the curve comprehensively, is put forword. Byexperimentally investigating a number of rats exposed to 80 mg SiO₂+20mg Fe₃O₄ particles, the variation law; of α^* vs. the time after exposure &/or death are gained. A highly significant linear negative correlation between the α^* values and the grade data got from the pathologic sections is discovered.