This study aimed to investigate the potential of exogenous enzymes treatment of tomato and watermelon crop byproducts (TCB and WCB, respectively) on gas production, rumen fermentation characteristics, and feed degradability using in vitro gas production method. Four different concentrations (0, 6, 12, and 24 mg/g) of ENZ were added with the substrate (TCB and WCB) inside the incubation tubes. Berseem hay substrate was used as a positive control. The results of chemical analyses of TCB and WCB showed that most of the nutrients are lower than those in berseem hay. The untreated WCB and TCB displayed a significant reduction in cumulative gas production (GP), microbial crude protein, short-chain fatty acid (SCFA), nutrient degradability, net energy (NE), and metabolizable energy (ME) contents. Still, they increased the partitioning factor value in comparison with berseem hay. However, increased GP, SCFA, ME, and NE with increasing ENZ levels were observed in both crop residues with a significant effect at the level of 24 mg/g. Also, the application of ENZ enhanced the degradation of dry matter (DM), crude protein (CP), and crude fiber (CF) compared with untreated WCB and TCB. All ENZ levels did not elicit any significant alterations in the ruminal pH, NH3–N concentration, and protozoa count. Conclusively, the results suggest that treatment of crop residues with ENZ, especially at 24 mg/g DM, could have the potential to improve the efficiency of feed utilization fed to ruminants, as evidenced by better gas production, in vitro DM, CF, and CP degradability.