The direct current polarographic behavior of 4n-BAR in dimethylsulfoxide as an aprotic solvent have been investigated. The reduction of 4n-BAR in 0.05M sodium perchlorate solution proceeds along two one-electron steps to give the corresponding compound containing hydrazo groups, each reduction wave was considerably diffusion controlled and irreversible. By addition of acid HAc to 4n-BAR in DMSO solvent, the two reduction waves have coalesced into one in the condition M ≥ mole ratio, acid/reductant(M = 2), the slope of log (id-i) (Mid / 2-i) / i vs. (-E) is irreversible along one-electron steps reduction waves.