[en] A new mercury standard for reactor neutron activation is prepared by using sulfhydryl cotton as a support to hold mercury. The preparation of cotton matrix is studied. It is compared with the mercury standard prepared by other methods. It's advantage is to obviate the loss of meacury in the preparetion and irradiation of the standard and to prepare easily. The mercury content is determined by neutron activation analysis with the mercury standard in U. S. NBS SRM-1645 and Japan NIES No. 2 Soil Standard Reference Material. Better precision and accuracy are obtained