Abstract: A new mercury standard for reactor neutron activation is prepared by usingsulfhydryl cotton as a support to hold mercury. The preparation of cotton matrixis 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 irradiationof the standard and to prepare easily. The mercury content is determined byneutron activation analysis with the mercury standard in U. S. NBS SRM-1645and Japan NIES No. 2 Soil Standard Reference Material. Better precision andaccuracy are obtained.