Decay protons from excited states in 21Na populated through a previously reported 24Mg(p,α)21Na transfer reaction [Cha et al., Phys. Rev. C 96, 025810 (2017)] were analyzed to extract the proton branching ratios of the energy levels. By utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched 24Mg solid targets, the decay protons were detected in coincidence with α particles from the (p,α) reaction using a silicon strip detector array. Proton decay branching ratios of several 21Na levels were deduced for the p0 and p1 decay channels to the ground and first excited states in 20Ne, respectively.