Event-related potentials (ERPs) were recorded on subjects who discriminated the stimulus duration of two sequentially presented spots (S1 and S2). Four kinds of trials were included: short-duration match (S1 and S2 lasting 300 ms), short-duration conflict (S1 and S2 lasting 300 ms and 600 ms, respectively), long-duration match (S1 and S2 were 600 ms) and long-duration conflict (S1 and S2 were 600 ms and 900 ms, respectively). When S1 was equal to S2, components of Pi, N1, P2, N2 and a delayed late positive component were recorded after the onset of S2. The other three negativities were elicited in both short and long duration conflict conditions. The three negative components peaked at 475, 600 and 900 ms in the short-duration condition, and they peaked at 805, 900 and 1200 ms in the long-duration condition. The first negativity was considered a visual mismatch negativity (vMMN), followed by a delayed N270 reflecting the conflict processing for duration in the brain. The last negativity, similar to N270, possibly reflects the second conflict processing activity evoked by stimulus offset.