Three new compounds, taraxacine-A (1), taraxacine-B (2) and taraxafolin (3), together with twenty-five known compounds, were isolated and characterized from the fresh aerial parts of Taraxacum formosanum. Taraxacum formosanum is a herbaceous plant belonging to the family Compositae, distributed mainly in the littoral areas of north Taichung in Taiwan. Some species of the genus Taraxacum have been used in folk medicine to treat lactation, and as diuretic, antimastopathy and anti-inflammatory agents. Earlier pharmacological studies on this plant revealed that the crude extract showed an in vitro bactericidal effect against Staphylococcus aureus and inhibitory action against Mycobacterium tuberculosis and Leptospira. It is also a relatively safe herb with an LD50 of 59 g/kg in mice and has a record of relatively few side effects. However, T. formosanum was hitherto uninvestigated for its chemical constituents. As a part of ongoing phytochemical work on Chinese medicinal plants, the aerial parts of T. formosanum were examined, which resulted in the isolation of three new and twenty-five known compounds. This paper deals with the structural determination of two new β-carbolines, taraxacine-A (1) and taraxacine-B (2), and one phenylpropanoid, taraxafolin (3) by means of spectral analysis. This is the first report of the isolation of β-carboline alkaloids from the genus of Taraxacum.