Spontaneous, reversible and repeatable shape change during heating and cooling ('two-way shape memory effect') of shape memory thin films can be used to actuate very minute mechanical devices. In this study, Ti 51.3 at.% Ni thin films were prepared by r.f. magnetron sputtering. After sputtering, they were first solution-treated at 973 K for 1 h. Subsequently, they were age-treated at various temperatures from 573 to 773 K for times of 1, 10 and 100 h, while the films were wound on to a stainless steel pipe (7.5 mm in outside diameter). These constrained-aging treatments gave all the thin films a two-way shape memory effect due to the R-phase transformation, but the transformation temperature and the degree of the shape change were found to be very sensitive to the aging conditions. The largest shape change due to the two-way shape memory effect is obtained above room temperature in the thin film aged at 773 K for 100 h. This film was found to be desirable for a small actuator.