Introduction: Soybean straw is an abundant but underutilized fibrous residue. This study tested the hypothesis that simultaneous inoculation of lactic acid bacteria (LAB) and cellulase would accelerate acidification and suppress undesirable microbes during micro-silage. Materials and Methods: Eight treatments (triplicated) were established: (1) straw+water (control); (2) straw+RS26 LAB; (3) straw+RS33 LAB; (4) straw+RS26+RS33; (5) straw+cellulase; (6) straw+RS26+cellulase; (7) straw+RS33+cellulase; (8) straw+RS26+RS33+cellulase. Chopped straw (60–65% moisture) was vacuum-sealed and stored at 20°C for 0, 8, 16, 32 and 64 d. pH was measured electrometrically; LAB, total bacteria, molds and yeasts were enumerated on MRS, NA and PDA plates. Results: Control pH remained 6.2 at 64 d. The pH of group 8 declined fastest, reaching 4.3 by 32 d and stabilising. LAB counts in group 8 rose from 10⁵ to 10⁹ CFU/g FM, while total bacteria fell from 10⁵ to 10³ CFU/g FM. No molds or yeasts were detected in any treated bags. Cellulase-supplied groups showed higher LAB proliferation and lower pH than cellulase-free groups. Conclusion: Co-inoculation of dual LAB strains plus cellulase rapidly acidified soybean straw silage, enriched LAB and eliminated spoilage fungi and yeasts, offering a safe, low-cost biopreservation strategy for on-farm feed use.