The present report describes the first isolation of monomeric N-alkoxyarylaminyls and their chemical and magnetic properties. Reaction of the corresponding lithium amides of 2,4-diaryl-6-tert-butylanilines, 2,6-diaryl-4-tert-butylanilines, or 2,4,6-triarylanilines with tert-butyl peroxybenzoate in THF at -78 degreesC yielded quite persistent N-tert-butoxy-2,4-diaryl-6-tert-butylphenylaminyls (1), N-tert-butoxy-2,6-diaryl-4-tert-butylphenylaminyls (2), and N-tert-butoxy-2,4,6-triarylphenylaminyls (3), respectively, which were isolated in the monomeric form in 17-25% yields. All radicals prepared were oxygen insensitive and thermally very stable. X-ray crystallographic analyses were carried out for two radicals, and it was shown that the N and O atoms are coplanar with the anilino benzene ring. The ESR spectra of 1-3 gave alpha (N) = 0.984-1.05 and alpha (H) (anilino meta) = 0.158-0.170 mT (g = 2.0041-2.0043), indicating that the unpaired electron mainly resides on the nitrogen and anilino benzene ring. Magnetic susceptibility measurements for 1 and 3 showed that one radical revealed a weak ferromagnetic interaction and an analysis by the Curie-Weiss law gave 0.3 K as theta. The other radicals examined showed weak antiferromagnetic interactions and theta 's were determined to be -0.3 to -1.5 K.