We consider the sharp interface limit of a coupled Stokes/Allen-Cahn system, when a parameter ε > 0 that is proportional to the thickness of the diffuse interface tends to zero, in a two dimensional bounded domain. For sufficiently small times we prove convergence of the solutions of the Stokes/Allen-Cahn system to solutions of a sharp interface model, where the interface evolution is given by the mean curvature equation with an additional convection term coupled to a two-phase Stokes system with an additional contribution to the stress tensor, which describes the capillary stress. To this end we construct a suitable approximation of the solution of the Stokes/Allen-Cahn system, using three levels of the terms in the formally matched asymptotic calculations, and estimate the difference with the aid of a suitable refinement of a spectral estimate of the linearized Allen-Cahn operator. Moreover, a careful treatment of the coupling terms is needed. Mathematics Subject Classification (2000): Primary: 76T99; Secondary: 35Q30, 35Q35, 35R35, 76D05, 76D45 Key words: Two-phase flow, diffuse interface model, sharp interface limit, Allen-Cahn equation, Free boundary problems 1 INTRODUCTION, MAIN RESULT, AND OVERVIEW is the jump of a function u : Ω × [0, T0] → R 2 at Γt in direction of nΓ t , HΓ t and VΓ t are the curvature and the normal velocity of Γt, both with respect to nΓ t . Furthermore, Dv = 1 2 (∇v + (∇v) T ) and σ = R θ ′ 0 (ρ) 2 dρ, where θ0 is the so-called optimal profile that is the unique solution ofIf the material derivative ∂tvε +vε ·∇vε is added to the right-hand side of (1.5) (i.e., the Navier-Stokes equations are considered), the system (1.5)-(1.9) was already suggested by Liu and Shen in [31] as an alternative approximation of a classical sharp interface model for a two-phase flow of viscous, incompressible, Newtonian fluids, which has advantages for numerical simulations since the Allen-Cahn equation is of second order and not of fourth order as the Cahn-Hilliard equation. On the other hand, for solutions of (1.5)-(1.9) the total mass Ω cε(x, t)dx is in general not preserved in time, in contrast to solutions of (1.1)-(1.4), which is a disadvantage if the model is used to approximate a two-phase flow without phase transitions. However, (1.5)-(1.9) can be considered as a simplified model for a two-phase flow with phase transitions. Such models can yield systems of Navier-Stokes/Allen-Cahn type, cf. e.g. Blesgen [11]. Finally, let us mention that in [31] a rigorous result on the sharp interface limes of (1.5)-(1.9) was announced, which was not published so far to the best of the author's knowledge.The limit system (1.11)-(1.16) was also studied by Liu, Sato, and Tonegawa in [30] if the Stokes equation on the right-hand side is replaced by a modified Navier-Stokes equation for a shear thickening non-Newtonian fluid of power-law type. They constructed weak solutions for this system using a Galerkin approximation by a corresponding Navier-Stokes/Allen-Cahn system. In the proof they pass to the limit in the Ga...