The paper deals with the effect of cooling rate on solidification behavior of IN 738LC nickel based superalloy and on resulting structural and chemical microheterogeneity of this alloy. Samples taken from as-received state were heated with controlled ramp rates (1, 5, 10 and 20 °C min-1). Immediately after melting they were cooled with the same controlled ramp rate with the help of the laboratory experimental system SETARAM SETSYS 18TM TG/DTA/TMA. Then the microanalysis of minority phases was conducted with use of X-ray spectroscopy and microstructure of the individual samples was documented by scanning electron microscopy. Chemical microheterogeneity was determined on the basis of measured concentration data of selected elements (Al, Ti, Cr, Co, Ni, Nb, Mo, Ta and W) in representative areas of the individual samples structure.