Three new tirucallane triterpenoids, $3{eta}$,16-dihydroxy-25-hydroperoxytirucalla-7,23(24)-dien-6-oxo acid (1), $3{eta}$,$16{eta}$-hydroxytirucalla-7,24(25)-dien-21,23-olide (2), and $3{eta}$,$16{eta}$-hydroxytirucalla- 7,24(25)-dien-6-oxo-21,23-olide (3) were isolated from the 70% ethanol extract of the stem bark of Melia toosendan. Their structures were determined on the basis of 1D and 2D NMR (COSY, HMQC, HMBC and NOESY) analyses. The isolated compounds were evaluated in vitro for cytotoxic activities against A549, SK-OV-3, SK-MEL-2 and HCT15 tumor cell lines. Compounds 2 and 3 exhibited significant cytotoxic activities against the four tested cell lines with $IC_{50}$ values of 3.4-5.7 ${mu}g/mL$ and 3.2-5.0 ${mu}g/mL$, respectively.