| Summary: | Seven resorcylic acid lactones (RALs) including five new analog rhinoclactones, A–E (<b>1</b>, <b>2</b>, <b>4</b>–<b>6</b>), were isolated from an endophytic fungus <i>Rhinocladiella similis</i> in the plant <i>Agriophyllum squarrosum</i> collected from the Tengger Desert of the Ningxia Province, China. The structures of these new compounds were determined by HR-ESI-MS (High Resolution Electrospray Ionization Mass Spectrometry), NMR data, modified Mosher’s method, and X-ray diffraction experiments. All compounds isolated from this fungus possessed the 16-OMe/14-OH, not the common 16-OH/14-OH or 16-OH/14-OMe groups on the aromatic ring, which are rarely found in nature. Compound <b>7</b> displayed cytotoxic activities against HCT116 and HeLa cancer cell lines. The possible biosynthesis of <b>1</b>–<b>7</b> is suggested, and the potential ecological roles of these fungal secondary metabolites is discussed.
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