Using the Nambu—Jona-Lasinio (NJL) model we study chemical potential response of the pion and kaon masses as a function of temperature and chemical potential, ie,∂ m∂ μ (T, μ). First, we obtain the responses assuming the vector—axial vector coupling is zero (g V= 0). Then, we include a non-zero g V and study the effects of g V on the responses. We find that the behavior of∂ m∂ μ for the pion is quite different from that for the kaon. It means that∂ m∂ μ is much dependent on the mass difference between the two quarks, ie, the u and s quarks (or even between the u and d quarks). Our results may give a clue to future studies of∂ m∂ μ on the lattice.