Acetone:chloroform (1:2) extract of the aerial parts of Euphorbia connata Boiss. (Euphorbiaceae) was investigated for its diterpenoids. This led to the isolation of one known and two new diterpenes, belonging to the pentahydroxy-13(17)-epoxy-8,10(18)-myrsinadiene and tetrahydroxy-5,6-epoxy-14-oxo-jatropha-11(E)-ene classes. The structures were elucidated based on (13)C and (1)H NMR as well as 2D NMR, IR and MS spectra and the cytotoxicity for compounds 1-3 were evaluated by using MTT assay against two human breast cancer cell lines. Myrsinane-type compounds - 3,7,14,15-tetraacetyl-5-propanoyl-13(17)-epoxy-8,10(18)-myrsinadiene (1) and 3,7,10,14,15-pentaacetyl-5-butanoyl-13,17-epoxy-8-myrsinene (2) - exhibited moderate inhibitory effects, with IC50 values of 24.53 ± 3.39 and 26.67 ± 1.41 μM against the MDA-MB cell line, and 37.73 ± 3.41 and 34.57 ± 2.12 μM against the MCF-7 cell line, respectively. Jatrophane-type diterpene - 5,6-epoxy-8,9,15-triacetyl-3-benzoyl-14-oxo-jatropha-11(E)-ene (3) - showed weak cytotoxicity, with IC50 values of 55.67 ± 7.09 μM against MDA-MB, and moderate cytotoxicity with IC50 values of 24.33 ± 3.21 μM against MCF-7 cell line.