A rare C-12-norabietane diterpene racemate (1) and a new abietane diterpene alkaloid (2) were isolated from the roots of Salvia miltiorrhiza Bunge. Their structures were established by comprehensive spectroscopic analyses, and 1 was successfully resolved by chiral HPLC, demonstrating that 1 is racemic. The absolute configurations of la [(+)-miltiorolide A], 1b [(-)-miltiorolide A], and 2 were determined using TDDFT-ECD calculations. la and lb are the first examples of enantiomeric C-12-norabietane diterpenes featuring an isobutylene with a tetrahydronaphthalene-butyrolactone ring system. The cytotoxic activities of the isolates (1 and 2) were evaluated against three human cancer cell lines BEL-7402, HT-29 and PANC-28. A plausible biogenetic pathway of 1 was also proposed.