The purpose of this study is to explore characteristics of on-line teaching materials on websites of natural history museums, particularly with regard to educational perspectives and the nature of science. The target resources were selected from the websites of the Natural History Museum in London, the Australian Museum in Sydney, the Field Museum of Natural History in Chicago, and the Smithsonian Museum in Washington D.C.. A total of twelve on-line resources from these museums used in this study were selected as representative informal science teaching materials. For the investigation, this study developed a checklist with a total of nine items that were grounded on mostly reviewing previous literature and articles focusing on educational perspectives of natural history museums and science centers. Exciting and positive results were found in all four museums. The analyses, however, indicated weaknesses as well as strengths in on-line resources regarding their usages as informal science teaching venues.