Three new trichostatin analogues, ulleunganilines A-C (<b>1</b>-<b>3</b>), and seven known trichostatins (<b>4</b>-<b>10</b>) were isolated from cultures of <i>Streptomyces</i> sp. 13F051. NMR, UV, and MS data indicated that the planar structures of <b>1</b>-<b>3</b> consisted of modified side chains in the trichostatic acid moiety. The absolute configuration of the 2,4-dimethyl-branched carbon chains in <b>1</b> and <b>2</b> was determined by the PGME method, while the amino acid group in <b>3</b> was identified by advanced Marfey's method. Based on the structure of the modified side chains, the origin of <b>1</b>-<b>3</b> is proposed. Further experiments indicated that <b>1</b> and <b>3</b> displayed moderate histone deacetylase inhibitory activity, suggesting that not only the hydroxamate group but also the <i>N</i>,<i>N</i>-dimethyl group were essential for the inhibitory activity.