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The preferential adsorption of targeted contaminants on a photocatalyst surface is highly required to realize its photocatalytic selective decomposition in a complex system. To realize the tunable preferential adsorption, altering the surface charge or polarity property of photocatalysts has widely been reported. However, it is quite difficult for a modified photocatalyst to realize the simultaneously preferential adsorption for both cationic and anionic dyes. In this study, to realize the selective adsorption for both cationic and anionic dyes on a photocatalyst surface, the negative reduced graphene oxide (rGO) nanosheets and positive phenylamine (PhNH) molecules are successfully loaded on the TiO surface (PhNH/rGO-TiO) with spatially separated adsorption sites, where the negative rGO and positive PhNH molecules work as the preferential adsorption sites for cationic and anionic dyes, respectively. It was interesting to find that although all the TiO samples (including the naked TiO, PhNH/TiO, rGO-TiO, and PhNH/rGO-TiO) clearly showed a better adsorption performance for cationic dyes than anionic dyes, only the PhNH/rGO-TiO with spatially separated adsorption-active sites exhibited an opposite photocatalytic selectivity, namely, the naked TiO, PhNH/TiO, and rGO-TiO showed a preferential decomposition for cationic dyes, while the resultant PhNH/rGO-TiO exhibited an excellently selective decomposition for anionic dyes. In addition, the resultant PhNH/rGO-TiO photocatalyst not only realizes the tunable photocatalytic selectivity but also can completely and sequentially decompose the opposite cationic and anionic dyes.