Abstract: The number, size, structure and form of A_gNOR particle of cell nucleus werestudied in 40 patients with breast cancer,were compared with 40 patients withbreast benign discease. The results showed that numbers of the large,small andmixed particle in the breast cancer group were significantly more than that in thecontrol group(P0.01).Specificity and sensitivity of quantitation on small particlewere 100% respectively. Differente of histologic type and malignant grade of breastcancer followed one of number. Structure and form of A_gNOR particle. The authorthought that it was very important value for diagnosis of breast cancer to determineexactly and rationally size of A_gNOR particle to use quantitative criterion of multiple parameters and ti combine with analysis of structure and form of A_gNOR particle,it was also helpful to judge malignant grade and prognosis of breast cancer.