Novel betulinderivatives were prepared and tested for their antitumoractivity. Starting from 3‐O‐acetyl‐ or 3‐O‐methyl‐betulinic aldehyde, the synthesis of C‐28 ethynyl derivatives was performed; their subsequent transformation with several 1,3‐dipolarophiles afforded pyrazoles and 1,2,3‐triazoles. Their screening for antitumoractivity was performed in a panel of 15 human cancer cell lines by a