Dipyrido[3,2-a:2′,3′-c]-phenazine (L) was employed as a selectively fluorescent chemosensor for Hg2+ in DMF solution under buffered conditions with its fluorescence being strongly increased. The fluorescence increasing was attributed to the formation of L–Hg2+ by 1:1 complex ratio (K=3.7×105 M−1), which constitutes the basis for the determination of Hg2+ with the prepared chemosensor. The experiment results also show that the response behavior of L to Hg2+ is pH independent in the range of pH 6.0–9.0 and show excellent sensitivity and selectivity for Hg2+ over other examined metal ions.