Seven commercial visible-light-cured (VL) dental composite resins were analytically studied for identification of the photo-initiator consisting of photo-sensitizer and reducing agent. Gas-liquid chromatography (GC) was used for the determination of the dilute components extracted from the composite resin. Mass spectroscopy (GC-MS) was used for confirmation of the qualitative data obtained by GC. The results showed that all composite resins examined included camphorquinone (CQ) as a photo-sensitizer. The concentration of CQ in the resin phase, however, ranged from 0.17 to 1.03% w/w. The composite resin with hybrid-sized filler tended to have a higher concentration of CQ than did the micro-filled composite resin. As for the reducing agent, two out of seven brands contained dimethylaminoethyl methacrylate (DMAEMA), and one included dimethyl-p-toluidine (DMPTI). The mixing ratio between CQ and the amine in these three composite resins also varied. Another four brands did not contain either DMAEMA or DMPTI, and would utilize different reducing agents.