Three new prenylated flavanones, (2S)-5,7,2'-trihydroxy-5'-(1''',1'''-dimethylallyl)-8-prenylflavanone (1), (2S)-5,7,2'-trihydroxy-8,3'-diprenylflavanone (2), and (2S)-5,2'-dihydroxy-6'',6''-dimethylchromeno-(7,8:2'',3'')-3'-prenylflavanone (3), and a known chromeno (dimethylpyrano) flavanone, obovatin (4), were isolated from the n-hexane extract of Dalea boliviana roots. The compounds were evaluated in vitro in relation to their inhibitory effect on the tyrosinase activity by using a spectrophotometric method.