Tanshinone IIA is derived from the dried roots of Salvia miltiorrhiza Bunge, a traditional Chinese medicine. Although Salvia miltiorrhiza has been applied for many years, the toxicity of the mono-constituent of Salvia miltiorrhiza, tanshinone IIA, is not been fully studied. In vitro analysis of the teratogenicity and embryo lethality of tanshinone IIA have been evaluated by using zebrafish embryos of removing chorions. After treated zebrafish embryos with tanshinone IIA for 4 days periods, the results showed that tanshinone IIA have teratogenic and lethal effects in zebrafish embryos. The LC₅₀ value is 15.1 µM, and when the concentration is beyond 20 µM, teratogenicity is manifested. The main endpoints of teratogenicity are scoliosis, malformation of tail, growth retardation, and pericardium edema. This study suggested the safe dose of tanshinone IIA might be low.