This study evaluates the potential use of the FBRM, ATR-FTIR, and Raman for on line detection of polymorphic transformation of carbamazepine (CBZ) during the cooling crystallization. Changes in solution concentration as a function of time were quantified from the ATR-FTIR data. A new quantitative method of polymorphs ratio was developed using Raman spectroscopy for in situ monitoring during a solution-mediated transformation of carbamazepine from form II to form III in 1-propanol. The polymorphic forms initially crystallized from solution, in the absence of seeds, could be clearly identified by FBRM and showed good agreement with results of microscopic images. Furthermore, the kinetics of the conversion of carbamazepine from metastable form to the stable form at different cooling rates could be readily followed.