Four naphthoic acid esters including a new compound were isolated from the roots of Rubia cordifolia L. The new one was named as rubilactone and its structure was elucidated as 3'-carbomethoxy-4'-hydroxy-naphtho[1',2'-2,3] pyran-6-one (I) based on the physicochemical properties and spectrometric analyses (UV, IR, MS, 1HNMR and 13CNMR). The other three were 3'-carbomethoxy-4'-hydroxy-naphtho [1',2'-2,3] furan (II), dihydromollugin (III) and 3-carbomethoxy-2-(3'-hydroxy)isopentyl-1,4-naphthohydroquinone-1-O -beta-D-glucoside (IV).