The objective of this study is to examine the effect of accelerator (NaNO3) on the strength properties of High volume Periwinkle shell ash blended cement concrete. A mix ratio and water-binder ratio of 1:2:4 (cement: sand: gravel) and 0.60, respectively was used as the reference. The cement was then replaced with 30% Periwinkle Shell Ash (PSA) by weight of cement. Sodium nitrate in the dosages of 1, 2, and 3% by weight of cement was added to the blended mixture of cement and PSA. The strength properties investigated were compressive and splitting tensile strength tested at 7, 14 and 28 days hydration. The results indicated that the compressive strength and the splitting tensile strength generally increases with curing age, and that sodium nitrate of up to 2% dosage greatly improved the strength performance of high volume PSA blended cement concrete over that of the reference. The study concluded that the inclusion of 2% sodium nitrate by weight of cement in the mixture could be considered the optimum dosage for the improvement of both compressive and splitting tensile strength of concrete incorporating up to 30% PSA content.