The n-type FZ silicon (P～1014/cm3) grown in hydrogen is irradiated with neutrons of the total flux of (2.9-6.0)×1017n/cm2 and with Cd ratio about 10 at room temperature. An S=1/2 EPR spectrum, labeled Si-PK2, is found in X band and at 77K. The angular dependence of the geff values with H in the (011) plane has a tricliuic symmetry. For one of the equivalent defect orientations the principle values of the g tensor and the direction cosines of the principle axes with respect to the cubic axes are as follows: g(±0.0004) n100 n010 n001 g1=2.0028 -0.5154 0.8473 -0.1283 g2=2.0063 -0.7386 -0.5151 -0.4347 g3=1.9971 -0.4344 -0.1293 0.8914 The simulated EPR spectra computed from the g tensor are consistent with the experimental results.The PK2 EPR spectrumappears in the unannealed neutron irradiated samples and remains until 300℃ annealing. It is probebly due to a kind of defects which is depen-tent of the hydrogen.