U.v spectra study of phosphacgclic compounds with tetracoordinated ring phosphorus atom has been an object of a rather limited number of WOZkS. There are only few works on U.V. absorption spectra of cyclic phosphonitriles which reveal a specifio character of their Π-electronic structure1; besides, there are some data on a significant low - frequency shifting of the electronic spectrum of 1.1 - diphenylphos-phabemene against that of benzene2. This communication presents an analyisis of the experimental findings on electronic absorption spectra of a Wide variety of substituted phospha-pyrimidines, PhP, (1,2,6 - phosphadiazines) for elucidating the nature of the observed absorption ban and for studying electronic distribution as well as separate characteristics of the php moLecules in the ground and excited states.