Department of Chemistry, University of Jodhpur, Jodhpur and Department of Pharmacology, S. N. Medical College, Jodhpur Manuscript received 28 June 1975, revised 12 August 1975, accepted 12 August 1975 Some new 10-N-acylamino phenothiazine& have been prepared and their ultraviolet and infrared spectra have been discussed. An attempt has been made to show the N-acyl substitution effects on the course of absorption pattern of phenothiazines, It was interesting to find that N-acyl substitution showed bathochromic shift in the U.V. spectra of these compounds and carbonyl peaks in the I.R. spectra have been shifted to higher region by 20-35 cm-1.