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Chemical investigation of secondary metabolites from the endophytic fungus <i>Pseudopestalotiopsis theae</i> led to the isolation of eighteen new polyketide derivatives, pestalotheols I&#8722;Q (<b>1</b>&#8722;<b>9</b>) and cytosporins O&#8722;W (<b>15</b>&#8722;<b>23</b>), together with eight known analogs (<b>10</b>&#8722;<b>14</b> and <b>24</b>&#8722;<b>26</b>). The structures of the new compounds were elucidated by HRMS and 1D and 2D NMR data, as well as by comparison with literature data. Modified Mosher&#8217;s method was applied to determine the absolute configuration of some compounds. Compound <b>23</b> showed significant cytotoxicity against the mouse lymphoma cell line L5178Y with an IC₅₀ value of 3.0 &#956;M. Furthermore, compounds <b>22</b> and <b>23</b> showed moderate antibacterial activity against drug-resistant <i>Acinetobacter baumannii</i> (ATCC BAA-1605) in combination with sublethal colistin concentrations.