A novel selective fluorescent chemosensor L based on rhodamine B derivative has been designed and synthesized to optically detect Cu²⁺ and S²⁻ in aqueous buffer solution. The fluorescence of L was excited by Cu²⁺ with a 1 : 1 binding ratio, and could be used as a “turn-on” type sensor. Otherwise, the emission band would undergo a slight red-shift. Once binding with Cu²⁺, the copper complex can exhibit high selectivity for S²⁻. Upon addition of Cu²⁺, the color of the chemosensor L changes from colorless to pink. Additionally, the resulting pink solution changes to colorless immediately upon the addition of S²⁻. However, no phenomenon change could be observed in the presence of other anions. Conclusively, the color changes suggest that sensor L could serve as a “naked-eye” sensor for Cu²⁺ and S²⁻.