The ternary uranium compound UCu2Sn with a hexagonal ZrPt2Al-type structure shows a phase transition at 16 K. We reported previously that huge lattice softening is accompanied by the phase transition, which originates from ferroquadrupolar ordering of the ground-state nonKramers doublet Γ5. A macroscopic strain, which is expected to emerge spontaneously, was not detected by powder x-ray diffraction in the temperature range between 4.2 and 300 K. To search the spontaneous strain, we have carried out thermal expansion measurements on a single-crystalline sample along the a, b, and c axes using a capacitance technique with the resolution of 10-8. In the present experiment, we found the spontaneous exx-eyy strain, which couples to the ground state doublet Γ5. The effect of uniaxial pressure along the a, b, and c axes on the transition temperature is also discussed.