Motivated by several proposed mathematical models of cell polarization, we studied reaction diffusion systems in which mass conserves through reactions. We found abrupt decays of stripes follow quasi stationary states sequentially in such systems. We give a stability condition of steady state that the system reaches after long transient time. It is also shown that there exist systems in which a single-stripe pattern is solely steady state for an arbitrary size of the systems. The applicability to cell biology is discussed. [1] S. Ishihara et al., Phys. Rev. E 75, 015203(R) (2007) [2] M.Otsuji et al., PLoS Comp. Biol. 3(6): e108 (2007)