Previous ERP studies using IAPS (International Affective Picture System) pictures have reported several ERP components (e.g., P1, N2, LPP) whose amplitudes are modulated by valence and arousal. But Bradley and her colleagues (2007) reported that early ERPs were modulated only by perceptual complexity, and only late ERPs (LPP) were modulated by affective factors. To elucidate the modulatory effect of perceptual complexity and affective valence of IAPS pictures on ERPs, we manipulated perceptual complexity and valence of them. Pleasant, neutral, and negative pictures from IAPS depicting either simple figure-ground compositions or complex scenes were selected. Each picture was presented for 2 s and participants were required to do valence discrimination response. 30-electrodes ERP data of 28 university students were analyzed. Mean amplitudes of early posterior P1 and P2, and LPP showed interaction effect of perceptual complexity and valence, and showed perceptual complexity effect only for neutral and positive pictures (no perceptual complexity effect for negative pictures). Time-frequence analysis showed similar results: Power of alpha and theta activities showed perceptual complexity effect only before 300ms, and showed the effect only for neutral and positive pictures. These results suggest that early ERPs can be modulated by affective valence and perceptual complexity only for neutral and positive pictures, and valence effect of negative pictures might override the effect of perceptual complexity.