Ten new terpenoids, including five diterpenoids (1-5), three nortriterpenoids (6-8), and two triterpenoids (9, 10), and 15 known terpenoids (11-25) were isolated from an acetone extract of Euphorbia soongarica. Sooneuphoramine (1) is the first example of a euphoractine B-type diterpenoid alkaloid, while sooneuphanones A-C (6-8) are rare nortriterpenoids from the Euphorbia genus. The isolated terpenoids were tested for their cytotoxicity and multidrug resistance (MDR) reversal activity, 10 of which showed moderate cytotoxicity against the KB and KBv200 cell lines, while 11 compounds exhibited P-gp modulating potential. The triterpenoid sooneuphanone D (9) possessed a remarkable MDR reversal activity much higher than the positive control, verapamil.