We have studied the effect of uniaxial pressure on the ferroelectric properties ofPbTiO3by using a first principles electronic structure method. The pressure is applied in theab-plane. The magnitude of the ferroelectric lattice distortion is found to increase as the pressure is increased. Short Ti-O bonds along thec-direction are found to remain almost constant in length whereas the stretched Ti-O bonds become more stretched because of an increase in the equilibrium lattice constant in thec-direction. The thermodynamic stability of the ferroelectric phase over the paraelectric phase increases as pressure is applied. ©2000 American Institute of Physics.