High-moisture grain silage is becoming increasingly important form of maize storage whereas additive addition is reducing the risk of undesirable fermentation and spoiling. It is not known whether additive addition affects digestibility kinetics of high-moisture corn, and this study aimed to explore the effect of inoculant and lactic acid during ensiling on starch digestibility rate in a model mimicking stomach and small intestine of the pig. Hybrid Bc 462 was ensiled in vacuum bags for 182 days spontaneously (control) and supplemented with Sil-All inoculant (Dr. Peiper, Germany) and lactic acid (0.9%). The extent of starch degradation in the in vitro model was determined after 15, 30, 45, 60, 120, 180, 240, 300 and 360 min. Starch and sugar contents were determined in all samples to calculate the starch digestibility kinetics. The addition of inoculant and lactic acid in high-moisture maize did not affect starch content and sugar in the silage. Dry matter digestibility of the samples ranged from 88.55% to 91.06% and did not differ between treatments. After the first two hours of incubation, on average 90.65% of starch was digested, and inoculant or lactic acid addition did not affect digestibility coefficients from the beginning to the second hour of incubation. The treatment had a significant effect on digestibility coefficients after three and four hours of incubation, and silages with inoculant addition had the highest values. At the same time, silage ensiled with inoculant had the highest proportion of potentially digestible fraction. Despite determined differences, treatment did not affect starch digestibility rate, and addition of inoculant and lactic acid resulted in numerically lower values compared to the control sample (1.02 vs. 1.29 l/h).