Thiosemicarbazide derivatives are widely used in medical practice as antituberculosis, antifungal, anticancer and other drugs. The biological activity of these substances is correlated to their structure. Therefore the synthesis and study of structural features of thiosemicarbazide derivatives are of both scientific and practical interest. The purpose of this study was to determine the crystal structures of 2 - (pyridine)-2-ylmethylene)No-tolylhydrazinecarbothioamide (I) and 2 - (pyridine)-2-ylmethylene)-Nm-tolylhydrazinecarbothioamide (II) by means of X-ray analysis. In both compounds, the substituents located on N-C bonds of the thiosemicarbazide azomethine fragment and N-C bonds are in the E-position (Fig. 1 and 2). The thiosemicarbazone fragments in both molecules are planar in the range of 0.015 Ǻ. In both molecules studied, the pyridine N atom of the cycle is in anti-position with respect to the N atom of hydrazine group, corresponding torsion angles are about 180 degree. In I and II, the bond lengths in the thiosemicarbazone fragments indicate their delocalization in these chains. The carbon atoms of methyl groups in both compounds are located in the planes of the pyridine fragments of the molecules. The two donor NH groups can form a system of H-bonds in molecules I and II.The reference molecule I forms donor (and acceptor) hydrogen bonds of N-H ... N = 3.074 Ǻ type with neighbouring molecules. Furthe, their development leads to the formation of a ribbon with the axis directed along the c axis of the crystal. Unlike (I), similar chains are formed in the crystal of compound (II) along the [010] direction, then they are combined with each other by H-bonds C-H ... S = 3.51 Ǻ. In addition to van der Waals interactions, there are X-H...Cg (p-ring) interactions between the chains, as well. The donor ability of I and II are also expressed in the formation of intramolecular H-bonds of the NH ... N and C-H ... S type. Thus, it has been shown that in the presence of bulky substitutents in the terminal nitrogen atoms, the conformation of the thiosemicarbazide fragment does not change. However, the substituent replacement in the second position of the phenyl cycle results in a nonplanar conformation of molecule II and changes in the crystal packing.figureFig. 1. The molecular structure of compound (I).Fig. 2. The molecular structure of compound (II).