Abstract: We study the acoustic limit from the Boltzmann equation in the framework of classical solutions. For a solution F_ε=μ+ε√μf_ε to the rescaled Boltzmann equation in the acoustic time scaling

∂_tF_ε+v·∇_xF_ε=ε⁻¹Q(F_ε,F_ε),

inside a periodic box T³, we establish the global-in-time uniform energy estimates of f_ε in ε and prove that f_ε converges strongly to f whose dynamics is governed by the acoustic system. The collision kernel Q includes hard-sphere interaction and inverse-power law with an angular cutoff.