In view of the fact that multi-store firms have been normal in a real society, this paper is concerned with the spatial decision of a multi-store firm under price regulation. It is shown that a multi-store firm with monopoly power will select as decision variables the size of a single store and the number of stores at the same time. In the duopolistic market, the new entrant will not compete with all stores of the incumbent on the same location, because of the non-existence of positive profit for both firms in this case. The new entrant will select to locate differently to compete with the incumbent in the short term. It is shown that there exists a Nash equilibrium regardless of whether or not the new entrant sets up its stores in the two ends of the linear market area. However, in the long run, the incumbent will decide not only the size of the stores, but also the locations. Nash equilibrium is shown to exist also in the long run. Finally, some numerical simulations of price regulation on welfare are carried out in the last section. Keywords¡Glocation, multi-store firm, price competition