Despite the substantial amount of asthma-related information available on the internet, little is known about the quality of such information. We assessed asthma-related information on the Korean internet intended as an educational material for asthma patients. By entering the key word, 'asthma', into 4 popular search engines, 32 web sites were identified and categorized with respect to authorship. The core asthma educational concepts and Health On the Net Code of Conduct principles were used to evaluate informational value and justifiability of unreliable information. Eight of 32 web sites were categorized as western physician, seventeen as oriental physician, four as commercial, and three as others. The mean number of core asthma educational concepts on the whole web sites was 2.7 out of 8. By type of authorship, 1.7 on the commercial sites, 2.1 on the oriental physician sites, 3.5 on the western physician sites, and 5.0 on the others sites in decreasing order. One of the western physician sites, two of the commercial sites, and all of the oriental physician and others sites contained unreliable information. However all of them except one site failed to satisfy our criteria of justifiability. Asthma-related information currently available on the Korean internet is highly variable in quality and lacks core asthma educational concepts and justifiability.