Biotransformation of betulonic acid (<b>1</b>) by <i>Rhizopus arrhizus</i> CGMCC 3.868 resulted in the production of 16 new (<b>3</b>, <b>5</b>, <b>6</b>, and <b>9</b>-<b>21</b>) and five known compounds. Structures of the new compounds were established by analysis of spectroscopic data. Hydroxylation, acetylation, oxygenation, glycosylation, and addition reactions involved the C-20-C-29 double bond. Antineuroinflammatory activities of the obtained compounds in NO production were tested in lipopolysaccharides-induced BV-2 cells. Compared with the substrate betulonic acid, biotransformation products <b>3</b>, <b>8</b>, <b>9</b>, <b>14</b>, and <b>21</b> exhibited an improved inhibitory effect, with IC<sub>50</sub> values of 10.26, 11.09, 5.38, 1.55, and 4.69 μM, lower than that of the positive control, <i>N</i><sup>G</sup>-monomethyl-l-arginine.