This study evaluated the use of domestic agro-food by-products, namely coffee grounds, herbal medicinal residues, and confectionery residues, as alternatives to imported substrate materials for oyster mushroom (Pleurotus ostreatus’Heuktari’) cultivation. Among six advanced mixed substrates (T1-T6), the T1 substrate comprising 50% hardwood sawdust, 20% beet pulp, 10% cottonseed meal, and 20% coffee grounds (v/v) achieved the highest yield (224 g/1,100 cc) and biological efficiency (108%). Field trials at commercial farms in Yeoju and Yangpyeong confirmed no statistically significant differences (p>0.05) in morphological quality or yield between the T1 and conventional substrates. In contrast, herbal medicinal residues were unsuitable for direct use because water-soluble inhibitors suppressed mycelial and contaminant growth. In conclusion, domestic coffee grounds can successfully replace 20% of conventional nutrient sources, providing an economical and sustainable approach to reducing substrate costs while promoting resource circulation in the mushroom industry.