<jats:title>Abstract</jats:title><jats:p><jats:italic>Papulaspora immersa</jats:italic> H. H. <jats:sc>Hotson</jats:sc> was isolated from roots and leaves of <jats:italic>Smallanthus sonchifolius</jats:italic> (<jats:sc>Poepp.</jats:sc> and <jats:sc>Endl.</jats:sc>) H. <jats:sc>Rob.</jats:sc> (Asteraceae), traditionally known as Yacon. The fungus was cultured in rice, and, from the AcOEt fraction, 14 compounds were isolated. Among them, (22<jats:italic>E</jats:italic>,24<jats:italic>R</jats:italic>)‐8,14‐epoxyergosta‐4,22‐diene‐3,6‐dione (<jats:bold>4</jats:bold>), 2,3‐epoxy‐1,2,3,4‐tetrahydronaphthalene‐<jats:italic>c</jats:italic>‐1,<jats:italic>c</jats:italic>‐4,8‐triol (<jats:bold>10</jats:bold>), and the chromone papulasporin (<jats:bold>13</jats:bold>) were new secondary metabolites. The spectral data of the known natural products were compared with the literature data, and their structures were established as the (24<jats:italic>R</jats:italic>)‐stigmast‐4‐en‐3‐one (<jats:bold>1</jats:bold>), 24‐methylenecycloartan‐3<jats:italic>β</jats:italic>‐ol (<jats:bold>2</jats:bold>), (22<jats:italic>E</jats:italic>,24<jats:italic>R</jats:italic>)‐ergosta‐4,6,8(14),22‐tetraen‐3‐one (<jats:bold>3</jats:bold>), (−)‐(3<jats:italic>R</jats:italic>,4<jats:italic>R</jats:italic>)‐4‐hydroxymellein (<jats:bold>5</jats:bold>), (−)‐(3<jats:italic>R</jats:italic>)‐5‐hydroxymellein (<jats:bold>6</jats:bold>), 6,8‐dihydroxy‐3‐methylisocoumarin (<jats:bold>7</jats:bold>), (−)‐(4<jats:italic>S</jats:italic>)‐4,8‐dihydroxy‐<jats:italic>α</jats:italic>‐tetralone (<jats:bold>8</jats:bold>), naphthalene‐1,8‐diol (<jats:bold>9</jats:bold>), 6,7,8‐trihydroxy‐3‐methylisocoumarin (<jats:bold>11</jats:bold>), 7‐hydroxy‐2,5‐dimethylchromone (<jats:bold>12</jats:bold>), and tyrosol (<jats:bold>14</jats:bold>). Compound <jats:bold>4</jats:bold> showed the highest cytotoxic activity against the human tumor cell lines MDA‐MB435 (melanoma), HCT‐8 (colon), SF295 (glioblastoma), and HL‐60 (promyelocytic leukemia), with <jats:italic>IC</jats:italic><jats:sub>50</jats:sub> values of 3.3, 14.7, 5.0 and 1.6 μ<jats:sc>M</jats:sc>, respectively. Strong synergistic effects were also observed with compound <jats:bold>5</jats:bold> and some of the isolated steroidal compounds.