Glass ornaments are imported artifacts widely found at Iron Age archaeological sites in Taiwan. Previous studies mostly focused on the provenance and exchange networks of the glass beads from the 1st millennium CE, whereas those of the 2nd millennium CE have not been well-studied. This study presents data on glass ornaments, including beads, rings, and earrings excavated from sites of Heping Island (2000-300 BP) in northern Taiwan. Most analyzed samples are beads belonging to the 2nd millennium and thus significantly fill a lacuna in current glass studies around the South China Sea region. Chemical composition and microstructural data were obtained using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and scanning electron microscopy - energy dispersive x-ray spectrometry (SEM-EDS). The results show that the samples can be divided into seven compositional groups, indicating diverse glass sources. Further comparison with previous research in Taiwan and beyond shows changes in the glass exchange networks from the early Iron Age to the 17th Century CE can be clearly observed. The dominance of m-Na-Al glass in the earlier period, and potassium lead silicate glass in the later period suggests a move from strong links to Southeast Asia, to a closer connection with China. This phenomenon has been suggested in Southeast Asia and Taiwan in previous studies and is further confirmed in this research. Moreover, within Taiwan, there are some specific styles of beads circulated in the northern and northeastern regions that indicate a possible local exchange network during the 2nd millennium, while there was no frequent exchange in the 1st millennium. In summary, this research increases our current understanding of glass circulation in the 2nd millennium CE in Taiwan as well as the South China Sea exchange networks.