Mercury that is fatal to the human body induced nervous system disorders and respiratory damage. Among various types of mercury species, methylmercury is well known to be the most toxic and lethal specie. In this research, I carried out design of fluorescent peptidyl probes and optimization of their detection ability for Hg2+ and CH3Hg+ in aqueous solutions. 10 dipeptidyl fluorescent probes using aggregation-induced emission were synthesized based on the previously reported fluorescent dipeptide probe for Hg2+ and their detection properties for Hg2+ and CH3Hg+ were compared. From this process, we found that TPE-AH-OH showed promising detection properties for Hg2+ and CH3Hg+ in aqueous solutions. The probe exhibited a selective and highly sensitive turn-on response to Hg2+ and CH3Hg+. The increased emission intensity of the probe by Hg2+ was more than twice as large as that of the previously reported probe. The probe employed in this research formed a 1:1 complex with Hg2+ and CH3Hg+, respectively. The Kd value was measured to be 3 nM (R²=0.95) for Hg2+ and 46.9 μM (R²=0.97) for CH3Hg+ using a nonlinear least square fitting of the fluorescence intensity change at 474 nm versus the concentration. The detection limit of the probe for Hg2+ ion was 5.9 nM, which was lower than the maximum allowable Hg2+ in drinking water regulated by EPA. The binding mode study proposed that selective interactions of Hg2+ ion with the peptide receptor part of the probe induced nano-sized aggregated, resulted in the enhanced fluorescent emissions.