Using a diamond-anvil cell and synchrotron X-ray diffraction, the compressional behavior of a synthetic qandilite Mg2.00(1)Ti1.00(1)O4 has been investigated up to about 14.9 GPa at 300 K. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yield an isothermal bulk modulus (KT0) of 175(5) GPa, with its first derivative K′T0 attaining 3.5(7). If K′T0 is fixed as 4, the KT0 value is 172(1) GPa. This value is substantially larger than the value of the adiabatic bulk modulus (KS0) previously determined by an ultrasonic pulse echo method (152(7) GPa; Liebermann et al. in Geophys J Int 50:553–586, 1977), but in general agreement with the KT0 empirically estimated on the basis of crystal chemical systematics (169 GPa; Hazen and Yang in Am Miner 84:1956– 1960, 1999). Compared to the KT0 values of the ulvöspinel (Fe2TiO4; ~148(4) GPa with K′T0 = 4) and the ringwoodite solid solutions along the Mg2SiO4–Fe2SiO4 join, our finding suggests that the substitution of Mg2+ for Fe2+ on the T sites of the 4–2 spinels can have more significant effect on the KT0 than that on the M sites.