Biological activities of pyridine derivatives have been successfully studied for various biological actions. Metal halide complexes of pyridine derivatives such as 2-chloropyridine, 2bromopyridine, 3-chloropyridine, 3-bromopyridine, 2-methoksipyridine, 2-(p-tolyl) pyridine, 2methylpyridine, 3-methylpyridine, 3,4-dimethylpyridine, 4-benzoylpyridine, 3-hydroxypyridine, 4ethylpyridine have been extensively studied [1]. However, the antitumor activities of these halide complexes have received less attention in the literature [2]. In this study, complexes with the general formula [PtCl2L2] (L: 3,4-dimethylpyridine, 2amino-3-methylpyridine , 2-amino-5-bromopyridine, 2-floropyridine) were synthesized and characterized via FT-IR, UV-Vis, 1H-NMR, 13C-NMR techniques. While the thermal behavior of the compounds was investigated via DTA/TG combined system, their kinetic parameters were investigated by using Flynn-Wall-Ozawa (FWO) and Kissenger-Akahira-Sunose (KAS) methods. The activation energies of the complexes were calculated to be 31,72- 196,54 kJ/mol for FWO and 29,17-203,43 kJ/mol for KAS. The cytotoxic effect of the complexes againts the colon cancer cell line (DLD-1), which is one of the most common types of cancer observed both in humans and animals, was investigated. The complexes showed high cytotoxicity. Especially, [PtCl2(2-floropyridine)2] and [PtCl2(2-amino3-methylpyridine)2] complexes were found to be the most effective compounds against colon cancer cell line during the 24 hours incubation period.