Abstract: K, values of 19 nuclides used in reactor neutron activation analysis are determined. These isotopes include 24Na,46Sc, 51Cr, 60Co, 50Fe, 65Zn,72Ga, 95Zr, 103Ru, 110mAg,122Sb,124Sb,l40La,141Ce,147Nd,181Hf,182Ta, 187W. The definition of K0 and measuring method are based on those of Simonits'with certain modifications, e.g, most irradiation target samples are prepared with solution dropped on the aluminum foil. The thermal flux and epithermal flux are obtained using the linear least square method by the activation rates of a set of isotopes instead of three isotopes or Cd-ration measurement. The irradiation period is about 10 hours.γ-rays are measured with Ge(Li) detector. The efficiency of detector is calibrated with standard γ-sources. The accuracies of K0 are less than 5%, These results agree with F. De Cortes' within 5% for most K0,