The Ramsey rule is regarded as a convenient vehicle for estimating the social discount rate in general. Carbon pricing is treated as another theory of environmental economics. This study clarifies the theoretical relationship between the Ramsey rule and optimal carbon price, which has been overlooked in the existing research. It succeeds in deriving the optimal carbon price from the modified Ramsey rule in stationary state. Since the Ramsey rule decides the dynamics of an economy and a stationary state is its destination, by using the optimization condition of individual who are assumed to live infinitesimally short life, we can solve the optimal carbon price at stationary state.