Magnetoresistance of (TMTSF)(2)ClO4 was investigated in the anion ordered s
tate (R-state), The angular dependence of magnetoresistance was measured fo
r l \\ c* and B \\ ab up to 24 T at 0.5 K. The third angular effect of magn
etoresistance quasi-one-dimensional (Q1D) metal was observed as the bump of
the magnetoresistance. Semiclassical calculation of the angular dependence
of the magnetoresistance was carried out based on a model Q1D conductor wi
th two pairs of Q1D Fermi surfaces as expected for (TMTSF)(2)ClO4 in the R-
state.