The microstructures of variously heat treated hypoeutectoid($0.45\%$ carbon) and eutectoid($0.85\%$ carbon) steel were characterized by magnetic coercivity measurement. The effect of spheroidization of cementites on the coercivity was investigated for $0.45\%$ carbon steel. In case of $0.85\%$ carbon steel, microstructural parameters such as prior austenite grain size, phase and pearlite interlamellar spacing were measured along with coercivity to investigate the relationships between them. Prior austenite grain size had little effect on the measured coercivity. Coercivity was observed to be high in order of martensite, pearlite and ferrite phases. The linear decrease of coercivity with increasing pearlite interlamellar spacing was found. The effect of each microstructural factor on the coercivity and the potential of coercivity as a nondestructive evaluation parameter for assessing microstructures of steel products are discussed.