[en] A study has been made of the electrostriction electromechanical coupling with due regard to dielectric nonlinearity. The electromechanical force factor k is expressed by the following equation: ksup(2)/(1-ksup(2)) approximately egual to (αsup(2)epsilonsup(0)sup(3)(1+5xiEsub(0)sup(2)))/(4πΛsup(D))Esub(0)sup(2). (1). To experimentally check this relationship, the field dependences of k, Λsup(D)-Young modulus and epsilon-reversible (differential permittivity) have been studied on polycrystalline solid solutions Basub(x)Srsub(1-x)TiOsub(3). It has been found that the proposed relationship (1) is suitable for calculating the value k