This paper proposes a novel micromechanics model tailored for dissolvable composites, where the inclusion undergoes dissolution and diffusion within the matrix, with the aim of analytically predicting the time-dependent properties of composites. The dissolution of inclusion leads to a reduction of its volume fraction and the formation of a growing interphase layer around the inclusion. This versatile model is applicable to both short-term dissolutions, as observed in the fabrication process of composites and long-term degradation occurring in high-temperature or corrosive environments, common in industrial and biological applications. Dimensionless expressions for time-dependent volume fractions of composite components are related to the dissolution and the diffusion rates, and a micromechanics three-phase model is established to evaluate the properties of the composite as a function of dissolution time. A detailed parametric study is performed to demonstrate the effect of all the parameters on the final properties. The model is successfully applied to the experimental data in the literature to show its capability and flexibility in predicting the practical dissolution examinations. The introduced model provides a pioneering framework for the future evolution of the dissolvable micromechanics concept.