The compositeness conditions of particles in quantum field theory are investigated in the case where two particles with identical quantum numbers can appear in the intermediate states of a certain scattering process as a consequence of the particle-mixing interaction. It is shown that, if we use the generalized propagator renormalization constants to state the compositeness condition, we encounter the curious situation first suggested by Srivastava and Choudhury, but, if we rely on the generalized wave-function renormalization constants, we can verify that the compositeness criteria still hold good in the presence of particle mixing.