A continuous precursor fiber bundle for manufacture of carbon fibers comprising a plurality of precursor fiber bundles each of which comprises at least 30,000 filaments, having a joined portion formed by joining at the terminal end of one of the precursor fiber bundles and the starting end of another one of the fiber bundles directly or through an intervening fiber bundle comprising a plurality of filaments, wherein the individual filaments at the joined portion are substantially uniformly interlaced with each other and wherein the interlacing of filaments is in a pattern selected from the group consisting of continuous substantially uniform interlacing in the transverse direction of said fiber bundles, interlacing at many joints on the joining portion, and interlacing of the entire face of said joining portion.