Thermal expansion in ZrTiO4 single crystal was investigated in the temperature range covering the normal, incommensurate, and commensurate phases. Remarkable change was found at the normal-incommensurate phase transition (T-I) in all thermal expansion coefficients a, b, and c. The spontaneous strains chi(as) and chi(bs) along the a and b axes show linear temperature dependence, while the spontaneous strain chi cs along the c axis shows a nonlinear temperature dependence. Small discontinuity along the c direction was observed at the incommensurate-commensurate transition temperature, T-c = 845 degrees C. dT(I)/dP and dT(c)/dP depend on the cooling rate.