Hydrogen sulfide (H2S) is constitutively generated in the human body and works as a gasotransmitter in synaptic transmission. In this study, we aimed to evaluate the roles of endogenous H2S in generating eupnea at the respiratory center. We employed an in situ arterially perfused preparation of decerebrated rats and recorded the central respiratory outputs. When the H2S-producing enzyme cystathionine β-synthase (CBS) was inhibited, respiration switched from the 3-phase eupneic pattern, which consists of inspiration, postinspiration, and expiration, to gasping-like respiration, which consists of inspiration only. On the other hand, when H2S synthesis was inhibited via cystathionine γ-lyase (CSE) or when H2S synthesis was activated via CBS, eupnea remained unchanged. These results suggest that H2S produced by CBS has crucial roles in maintaining the neuronal network to generate eupnea. The mechanism of respiratory pattern generation might be switched from a network-based system to a pacemaker cell-based system in low H2S conditions.