In the two-dimensional organic conductor, tau-(EDO-S,S-DMEDT-TTF)(2)(AuBr2)(1+y), we have observed Shubnikov de Hass oscillations with Landau level down to n = 2 in field up to 27 T. Motivated with this result, we extended to Hall effect study in pulsed magnetic field up to 60 T as well as in do field up to 45 T and found Hall resistance plateau above 40 T (n = 1). Since this system consists of two two-dimensional Fermi surface pockets, and larger pocket has a large effective mass compared with the smaller one, larger Fermi pocket behaves as a reservoir for the smaller pocket to be well-separated into completely filled and completely empty Landau levels in a certain range of temperature and magnetic field. The interpretation of realizing the Hall plateau can be understood as a new mechanism for QHE, but is quite different neither from localization nor field induce spin density wave state in organic TMTSF salts. (C) 2004 Elsevier B.V. All rights reserved.