This study explores using a low transition temperature mixture (LTTM), containing sulfamic acid and ethylene glycol for the pretreatment of corn straw and sorghum biomass, aimed to improve the efficiency of converting biomass into platform chemicals. We first optimized the pretreatment conditions (solid-liquid ratio, temperature, and time) and assessed the conversion of pretreated biomass into 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA) using the catalyst Amberlyst-15. Optimal pretreatment conditions were found to be a solid-liquid ratio of 1:5 (w/w), a temperature of 40 °C, and a duration of 4 hours, which resulted in the highest yields of sugars; xylose, glucose, and sucrose. In the catalytic conversion of sorghum and corn straw pretreated with LTTM at 200 °C in the presence of Amberlyst-15, 801.2 ppm glucose and 1967.3 ppm levulinic acid were obtained from sorghum, while 663.9 ppm glucose and 1936.3 ppm levulinic acid were produced from corn straw. The study demonstrates that LTTMs offer effective and sustainable biomass pretreatment, improving the accessibility of lignocellulosic structure to catalysts, leading to higher yields of desired products like glucose and levulinic acid.