  We consider the Josephson effect when two independent Bose superfluids are
weakly connected. In the presence of interparticle interaction and based on the
calculations of the one-particle density matrix of the whole system, we find
that the one-particle density matrix can be factorized which satisfies the
general criterion of Bose superfluid proposed by Penrose and Onsager. By
introducing an effective order parameter for the whole system, our researches
show that there is Josephson effect for two independent Bose superfluids.
