Steady-state and time,resolved fluorescence techniques were employed to study the excited-state proton transfer (ESPT) from a photoacid adsorbed on starch to a nearby water molecule. Starch is composed of similar to 30% amylose and similar to 70% amylopectin. We found that the ESPT rate of adsorbed 8-hydroxy-1,3,6-pyrenetrisulfonate (HPTS) on starch arises from two time constants of 300 ps and similar to 3 ns. We explain these results by assigning the two different ESPT rates to HPTS adsorbed on amylose and on amylopectin. Whesi adsorbed on arnylose, the ESPT rate is similar to 3 x 10(9) s(-1), whereas on amylopectin, it is only x 10(8) s(-1).