Titration method (dropping-on method) was introduced as an efficient approach for determining the mercury ion (Hg2+) concentration in aqueous solution by using fabricated cellulosic paper-based test strips. In this study, dithizone used as a recognition reagent was physically loaded on cellulosic paper-based test strips for Hg2+ selective recognition. The sensing mechanism was established on the spectral absorption rate of the coordination compound that was formed by dithizone and Hg2+ under strong acidic conditions. The calibration curve was obtained by the absorbency of Hg2+-dithizone complexes from different Hg2+ concentration solutions, and the correlation coefficient (R 2) reached 0.9971. The detection range of the test trip for Hg2+ was obtained at 0.1 μg/mL to 30 μg/mL. Moreover, these superior cellulosic paper-based test strips have a rapid color-forming time (1.5 min) and low volume demand (3.7 μL samples at 0.0127 g/L dithizone recognition concentration). This portable paper-based test strip can give potential applications for field screening or on-site semiquantitative analysis.