We identify an isotopic dependence of residual zonal flows from an analytic calculation. While the well-known Rosenbluth–Hinton residual zonal flows with radial scale greater than the magnetically trapped ion radial width ρbi have no isotopic dependence (Rosenbluth and Hinton 1998 Phys. Rev. Lett.80 724), we find that shorter radial scale (shorter than ρbi, but larger than the magnetically trapped electron radial width ρbe) residual zonal flows (Wang and Hahm 2009 Phys. Plasmas16 062309) exhibit isotopic dependence. These finer scale zonal flows in deuterium (D) plasmas can be stronger than those of hydrogen (H) plasmas, and possibly lead to lower turbulence and transport and better confinement in qualitative agreement with experimental results.