This study was designed to evaluate the effect of applying lactic acid bacteria (LAB, Lactobacillus plantarum LP) (0 and 1 × 106 cfu/g fresh matter (FM)) and cellulase (0, 30, 60 and 120 U/g FM) on the ensiling characteristics of N. cadamba leaves. The experimental design was a completely randomized 2 × 4 factorial arrangement. Fermentation parameters, microbial populations, chemical compositions and in vitro digestibility of the silages were measured after 60-day fermentation. LAB inoculation decreased the pH (p < 0.05), ammonium nitrogen (NH3-N) proportion (p = 0.08), the concentrations of crude protein (CP, p < 0.05) and condensed tannins (CT, p = 0.07), and the microbial counts (p < 0.01) of LAB and yeasts along with increased (p < 0.01) concentrations of neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL) and hemicellulose. Cellulase addition increased (p < 0.01) the microbial populations and protein fractions and decreased (p < 0.01) the concentrations of acetic acid, cell wall components, total phenols (TP), soluble tannins (ST) and CT with increasing enzyme inclusions. The interaction of LAB and cellulase showed an effect (p < 0.01) on the NH3-N proportion, microbial counts, fibre fractions and CP. No effect (p > 0.05) was found on the dry matter recovery and digestibility of the silages with LAB or cellulase application. Besides, high lactic acid concentration and true protein ratio, low pH and NH3-N proportion, and a few spoilage organism counts were found in all silages, indicating a successful preservation. These results infer that, with some improvement, the ensiling characteristics and chemical compositions of N. cadamba leaves silage show specific responses to the addition of LAB inoculant or cellulase.