Abstract: Single crystals of 2,2, 6, 6-tetramethyl-4-hydroxypiperidine (1) were prepared, in which the 2, 2, 6, 6-tetramethyl-1-hydroxypiperidine-l-oxy radical was as an impurity. The Atensor of nitroxide radical cited above (2) has been determined and the eigenvalues of tensor Aare calculated to be 7.2, 5.2, and 33.8 Grespectively. The ESRspectra of (2) observed indicate the existence of six lines corresponding to two types of paramagnetic centers with different orientations in the matrix of (1), each of which contributing its triplet.