The present investigation has evaluated advantages and disadvantages of using sodium carbonate (soda ash) or sodium hydroxide (caustic soda) as an alkali source in the alkaline peroxide mechanical pulping (APMP) of wheat straw. The soda ash-based alkaline peroxide impregnation offered savings in chemical cost, gave higher pulp yield, and resulted in smaller amounts of dissolved organic substances in the spent bleaching liquor, i.e. lower COD discharge. On the other hand, the caustic soda-based alkaline peroxide impregnation produced a brighter and stronger pulp. The choice of soda ash or caustic soda should, to a large extent, be determined by the end-use requirements of pulp properties, optical and physical.