Three new cytotoxic 10,13-cyclotrichothecane-derived macrolides, myrothecines A-C (1-3), were characterized from the extracts of two Myrothecium roridum strains, IFB-E009 and IFB-E012, isolated as endophytic fungi found on the traditional Chinese medicinal plants Trachelospermum jasminoides and Artemisia annua, respectively. The absolute configuration of myrothecines A-C was elucidated by a combination of spectral techniques (UV, IR, MS, circular dichroism (CD), (1)H and (13)C NMR, DEPT, (1)H-(1)H COSY, NOESY, HMQC, and HMBC spectrascopic analyses), Mosher's ester analysis, and single-crystal X-ray diffraction. The absolute configuration of the reported bioactive analogue, mytoxin B was established by correlating its spectral data with that of known absolute configurational structures. Furthermore, the significance in endophytism (or symbiosis) and biocatabolism, highlighted by production of those macrolides by the endophytic strains, is discussed in brief.