The rate of homogeneous vapor-liquid nucleation is controlled mainly by the Gibbs formation free energy of critical clusters. Within the framework of the i/v cluster theory of Reiss and co-workers, the formation free energies of Stockmayer clusters in the presence of a uniform electric field are determined. The Helmholtz free energy of the clusters, an input required in the i/v cluster theory, is calculated via Monte Carlo simulations. The most significant result is that as a uniform electric held is applied the formation free energy at fixed supersaturation of the vapor becomes larger than that in the absence of a field, whereas at fixed chemical potential the formation free energy becomes smaller.