A polar molecular gas with a strong dipolar interaction is a system of great interest to both the atomic and molecular physics and condensed-matter physics communities due to the versatile and promising potential applications. With controllable, anisotropic and long range dipole–dipole interactions, they could be used in quantum computation, quantum simulation, precision measurement and controlled cold chemistry. Here we study the stability of trapped NaRb, NaCs and RbCs molecular BECs. For these molecules their electric dipole moments can be polarized by an external electric field. As the applied electric field increases, the dipole moment d continuously increases from zero to the permanent dipole moment. We model the dipolar BEC using the mean-field Gross-Pitaevskii equation (GPE). We find that for a particular molecular BEC, the maximum number of molecules for which the condensate will remain stabilized depends on (i) value of dipole moment, (ii) value of contact interaction scattering length. We have also studied the case when the polarizing field is perpendicular to the trap axis.