A new naphthoquinone, 6-methoxy-7-hydroxy-α-dunnione (1), along with four known compounds (2, 4, 10, and 11) were isolated from Snningia canescens (Mart.) Wiehler tubers, while S. warmingii (Hiern.) Chautems furnished eight known compounds (3–10). The known compounds were identified as 7-hydroxy-α-dunnione (2), lapachenole (3), tectoquinone (4), 7-methoxytectoquinone (5), 1-hydroxytectoquinone (6), 7-hydroxytectoquinone (7), aggregatin C (8), aggregatin D (9), halleridone (10), and cedrol (11). In addition, S. canescens yielded a volatile fraction, which was analyzed by GC/FID and GC/MS. This fraction was constituted mainly by sesquiterpene hydrocarbons (82.6%). The major components were β-santalene (14.6%), β-cedrene (10.4%), and trans-cadina-1(6)-4-diene (10.0%).