Abstract: A process for continuously producing carbon fibers which comprises interconnecting the rear end of a preceding precursor fibrous yarn with the front end of a subsequent precursor fibrous yarn and continuously calcining the successively interconnected precursor yarns. In said process, said rear end and said front end are doubled on each other so that said successive precursor yarns are connected with each other by means of a length of doubled portion or each of said rear and front ends is doubled on each end of a different type fibrous yarn capable of being calcined so that said successive yarns are connected with each other through said different type yarn by means of lengths of doubled portion, and said yarns are entangled at the doubled portion to integrally interconnect said successive precursor yarns, a tensile strength of said doubled and entangled portion after oxidation in an air atmosphere at about 230.degree. to 250.degree. C. for 100 to 200 minutes is at least 0.8 g/d.