The effects of Earth's rotation on the stability of a thermohaline front of finite width are studied by means of a linear theory. It is found that when the rotation is present, two different types of unstable modes are possible. When the front is narrow and a Rossby radius of deformation based on Ruddick and Turner's (1979) vertical scale is large in comparison with the width of the front, the fastest growing intrusion is nearly two dimensional (nonrotational mode), and its vertical scale is given by Ruddick and Turner's scale. When the Rossby radius becomes small, in addition to the nonrotational mode there appears another unstable mode (the rotational mode) which has a smaller vertical wave number than the nonrotational mode. With the introduction of rotation, the fastest growing mode has nonzero along-frontal wave number; that is, the intrusion becomes-tilted in the along-frontal direction. When the Rossby radius of deformation is sufficiently small in comparision with the width of the front, to rotational mode becomes less pronounced when the width of the front is increased for fixed horizontal density-compensating gradients of temperature and salinity. For a wide front the growth rate and vertical wave number for both modes becomes similar, which agrees with the results of previous studies for infinite fronts that rotation does not modify the behavior of the intrusion except for the occurrence of along-frontal tilt. ¿ American Geophysical Union 1989