A combination tool holder includes a holder body, at least one tool adapter and a bolt. The holder body defines therein a through hole including an enlarged-diameter segment, a reduced-diameter segment and a tapered segment. A stepped surface is formed between the enlarged-diameter segment and the reduced-diameter segment. The tool adapter defines therein a channel and has a combining end. The combining end has a conical surface configured to be received in the tapered segment. The bolt includes a screw and a nut. The nut is configured to abut against the stepped surface while the screw extends into the tapered segment to engage with the combining end. By screwing the bolt, the conical surface is driven to press against the tapered segment, making the through hole and the channel coaxial.