We have successfully demonstrated a polymer electrolyte membrane (PEM) composed of core-shell type nanoparticles (NPs) which are silica NPs coated with poly(acrylic acid)-b-polystyrene (PAA-b-PS). In this work, for further improvement of proton conductive performance, we focus on the relationship between the coating amount of PAA and proton conduction performance. The PAA coating amount can be facilely controlled by changing the polymerization conditions. With the optimized PAA coating amount, the proton conductivity shows 9.2 × 10-4 S cm-1 at 60 °C and 98% relative humidity with low activation energy (E a = 0.33 eV). In addition, with coating PS on silica@PAA, silica@PAA-b-PS shows the proton conduction performance in a wide humidity range. It suggests that coated PS prevents the PAA swelling and suppresses flowing moisture out from the membrane. This report indicates that core-shell type NPs show great potential for a good PEM membrane in various operation conditions by simple polymerization conditions.