The macroscopic behavior of reaction–diffusion systems in inhomogeneous media is investigated theoretically. The phenomenological reaction–diffusion equation describing spatial and temporal evolution of the coarse-grained density is derived for systems where reactions take place only on the surface or in the inside of spherical static catalysts immersed dilutely. General cases of one-component reactions and two examples, X+Y→products and X⇄Y, Y+Y→ products, of multi(two)-component systems are considered. It becomes evident that in general, the phenomenological reaction–diffusion equation has a different functional form from that of the microscopic reaction–diffusion equation. In addition, it should be emphasized that accordingly as D→∞ or D→0, where D is a diffusion coefficient of reactants, the process exhibits two asymptotic behaviors, the reaction-controlled behavior and the diffusion-controlled behavior. In the reaction-controlled region, the system is homogenous on a macroscopic scale and the density dependence of the phenomenological equation is identical to that of the microscopic equation. In the diffusion-controlled region, the coarse-grained density follows the Smoluchowski-type linear reaction–diffusion equation and decays exponentially for all cases regardless of the type of reactions. At intermediate regimes, the phenomenological equation is generally a nonanalytic function of the density and the system shows a complex space and time dependence. In case of the bimolecular reaction, X+X→products, for instance, the crossover from the expontential to the algebraic decay is observed. The existence of more than two limiting behaviors in multicomponent reactions is also elucidated but their essential features are same as those of one-component systems. It is argued that asymptotic properties clarified here are universal phemomena found in a wide variety of real inhomogeneous systems.