Better understanding the decomposition and dissolution behaviors of limestone under steelmaking condition is essential to evaluate the possibility of directly using limestone instead of lime in converter. In this paper, the decomposition behavior of limestone in early converter slag including the decomposition kinetics and microstructure of the produced lime layer were studied, and the effects of slag temperature and stirring speed introduced to the slag bath were examined. Kinetic analysis based both on shrinking core model and dimensionless chemical heat transfer number (Nal) showed that the limestone decomposition at 1300-1400 degrees C was a mixed control of chemical reaction and heat conduction through the lime layer. Slag temperature has a significant influence on the decomposition process while the stirring speed plays a minor role when a critical stirring intensity is reached. The obtained effective thermal conductivity varied from 021 to 2.51 W m(-1) K-1 and the chemical reaction rate constant ranged between 7.9 x 10(-4) and 63 x 10(-3) m s(-1). The produced lime layer has less grain size and apparent porosity than the calcined one. Besides, smaller limestone particle and more heat supply to the converter bath are recommended to accelerate the limestone decomposition in early converter slag. (C)2017 Elsevier B.V. All rights reserved.