The linear and nonlinear optical properties of trans-cisoid saturated and unsaturated polyarninoborane/ polyphosphinoborane alternating copolymers are studied at the MP2/6-311G(2d)//PBEO/6-31G(2d) level of approximation, by using the increasingly large oligomer series methodology. We report the evolution with chain length of geometry parameters, partial atomic charges, electric dipole moments, polarizabilities and first hyperpolarizabilities of both phosphorus-and nitrogen-terminated chains. It turns out that for the saturated copolymer, linear and nonlinear optics properties of the saturated copolymer correspond to an average of the response of polyarninoborane and polyphosphinoborane. For the conjugated copolymer, the response is guided by the least delocalizable component.