Efficient secondary refining process is necessary for massive and stable production of low carbon aluminum-killed (LCAK) steels. Plant trials were performed to investigate the cleanliness of steels. Characteristics of composition, cleanliness, and inclusions of LCAK steel during different secondary refining processes, including LF, CAS, RH-LIT, and RH, were studied and compared. The results showed that CAS, RH-LIT, and RH processes had better control of low carbon, silicon, and nitrogen than LF process. High cleanliness of LCAK steels could be achieved by all the mentioned refining processes. It was concluded that the total oxygen (T.O.) should be <35 ppm to reduce the amount of inclusions and reach the level of clean steels. The removal rate of inclusions during RH-LIT and RH processes was much higher than that of LF and CAS. The T.O. content and the amounts of inclusions during CAS, RH-LIT, and RH could be quickly decreased to a low value within 10 min. The results showed that CAS and RH-LIT as well as RH refining processes can produce LCAK steels that meet the requirements of high efficient, low cost, clean, and stable production, while LF is more suitable for the heats with poor control of end point of BOF, and for the process with calcium treatment to control sulfur content and lower the clogging of Submerged Entry Nozzle during thin slab continuous casting.