Spent coffee ground (SCG) is the waste generated during the preparation of instant coffee and is the source of industrially valuable organic compounds. In this article, SCG was pretreated by roasting at 150°C for 30 minutes and heated with water at 90°C for extracting carbohydrates and phenolic compounds, after which 1.0% (w/w) β-mannanase was applied for the hydrolysis of pretreated SCG. SCG is characterized in terms of its total sugar content by the anthrone-sulfuric assay and phenolic compounds by Folin−Ciocalteu's procedure. In this study, the total sugar increased by 14.79% (w/w) by the roasting process, and subsequently enzymatic hydrolysis increased the total sugar yield up to 17.43% (w/w) compared to the untreated SCG, i.e., 10.24% (w/w). The reducing sugar was estimated by the dinitrosalicylic acid method and the end product increased to 106.10 (mg Glucose/g) from the initial content 5.32 (mg Glucose/g raw SCG). The total phenolic compound increased to 291.86 (mg Gallic acid/g lyophilized material), which was a 6.39-fold increase compared to the native SCG (45.68 mg Gallic acid/g). These results point to the valuable compounds present in SCG, can be enhanced by combining the roasting pretreatment and enzymatic hydrolysis, and can be utilized in the food and biotech industries.