The transport properties of organic tau-type conductors seem to be very clean as well as very dirty depending on what we observe. To clarify this problem, we studied temperature and magnetic field dependence of resistivity, rho(T, B), in tau-(EDO-S,S-DMEDT-TTF)(2)(AuCl2)(1+y). The properties that favor "probably dirty" are: i) stepwise rho(a)(T) increase below 20 K, which is suppressed by magnetic field, and ii) contrasted difference in rho(T) as well as magnetization M(T) between field cooled (FC) and zero field cooled (ZFC). On the other hand, Shubnikov de Haas oscillations with very low Dingle temperature (T-D = 1.5 K) are typical of clean system. Based on these observations, we conclude this system changes from "dirty" to "clean" system by increase of magnetic field.