Abstract: The non-solvated crystalline form "A" of 3-(-4-cynnamyl-1-piperazinyl)-iminomethylrifamycine SV finds application in the therapeutical practice.It represents a crystalline substance with absorption maximum of the infrared spectrum at 1644, 1585, 1340, 1350, 1295 and 1290-doublet, 1238, 1213, and triplet with low intesitivety at 726, 735 and 760 cm.sup.-1, as well as with characteristic diffraction maxima at 9,25 and 9,50 .theta.--most-intensive at 12,22 and doublet at 13,10 and 13,33 .theta. of the X-ray diffraction diagram.The obtaining of the non-solvated crystalline form "A" consists in the isolation of 3-(-4-cynnamyl-1-piperazinyl)-iminomethylrifamycine obtained in medium of indifferent organic solvent, preferably tetrahydrofuran or chloroform, and its dissolution in isopropanol or acetone or a mixture of both at a temperature from 30.degree. C. up to the ebullition temperature of the respective solvent.