The linear-chain insulating antiferromagnet KFeS2, is one of the first ternary alkali metal thioferrates [1]. It is considered as a model one-dimensional magnetic system and as a spin analog of the iron-sulfur ferrodoxin proteins. The compound contains chains of the edge-shared FeS4 tetrahedra separated from and bound to each other with K atoms [2]. In spite of numerous previous studies, the origin of the spin state of KFeS2 still remains unclear. We have grown KFeS2 single crystals by the Bridgman method and carried out a detailed study of their structural and magnetic properties. The composition of the sample was determined by the wave-length dispersive X-ray electron-probe microanalysis (WDS, Cameca SX50) which found only small deviation from the ideal stoichiometry corresponding to K1.065(30)Fe0.986(25)S2.000(33). From the analysis of the powder X-ray diffraction no additional reflections of impurities phase were found. The main structural parameters, such as lattice constants (a=7.075Å, b=11.315Å, c=5.388Å) were determined within the monoclinic space group C12/c1. The magnetic measurements show a nonlinear increase of the susceptibility in the AFM state (for configuration H ll c) up to 240 K and a sharp transition into paramagnetic state at TN~250 K. Above 250 K, the susceptibility shows a linear increase with temperature up to 400 K. For configuration H _ c, the susceptibility shows only shallow minimum at TN and flattens of further decrease of the temperature down to 100 K.