A new cycloheptapeptide, integerrimide C (1), which exhibited significant cytotoxic activity against tumoral KB cells (IC50 1.7 μM), was isolated from the ethyl acetate extract of the latex of Jatropha integerrima. The structure was elucidated on the basis of the MS/MS fragmentation using a Q-TOF mass spectrometer equipped with an ESI source, chemical degradation and extensive one and two dimensional nuclear magnetic resonance.