The solidification structure, microstructure evolution during rolling and precipitates with nanometers in dimension of thelow carbon steels produced by CSP process with thin slabs have been studied in recent years. Important differences in microstructureand mechanical properties between the CSP products and the conventional one were observed. These differences may arise from themuch rapider solidification rate and cooling rate after casting of the thin slabs. Some aspects of the microstructure for the low carbonsteels of the CSP thin slabs are summarized and compared with the conventional one.