AbstractFluid‐rock dissolution occurs ubiquitously in geological systems. Surface‐volume scaling is central to predicting overall dissolution rate R involved in modeling dissolution processes. Previous works focused on single‐phase environments but overlooked the multiphase‐flow effect. Here, through limestone‐based microfluidics experiments, we establish a fundamental link between dissolution regimes and scaling laws. In regime I (uniform), the scaling is consistent with classic law, and a satisfactory prediction of R can be obtained. However, the scaling for regime II (localized) deviates significantly from classic law. The underlying mechanism is that the reaction‐induced gas phase forms a layer, acting as a barrier that hinders contact between the acid and rock. Consequently, the error between measurement and prediction continuously amplifies as dissolution proceeds; the predictability is poor. We propose a theoretical model that describes the regime transition, exhibiting excellent agreement with experimental results. This work offers guidance on the usage of scaling law in multiphase flow environments.