This study was carried out to determine the effect of the age of the leaves and fermentation on in vitro protein digestibility and biochemical properties of leaves powder of Moringa oleifera. A 6 × 2 × 2 factorial design with two ages of the leaves (one and seven-month-old leaves), six times of fermentation and two fermentation temperatures was used for this purpose. One and seven-month-old fresh leaves were dried at 45 ℃ for 24 h, crushed to 1000 μm then fermented at 30℃ and 37℃ for 120 hours with Lactobacillus plantarum A6 at 10⁸ CFU/g. Samples were withdrawn every 24 hours for physico-chemical analyses. Results showed that 7 month-old leaves were richer in iron, proteins, polyphenols and phytates than one month old leaves. The phytates content dropped from 66.92% and 61.95% in the seven and one month-old leaves powders respectively fermented at 37℃, and from 54.15% and 67.95% in the seven and one month-old leaves powders respectively fermented at 30℃. Protein content increased by 26.34% and 24.48% for the 1and 7-month-old leaves powders respectively fermented at 37℃, and by 13.06% and 13.97% for the 1and 7month-old leaves powders respectively, fermented at 30℃. Iron availability increased from 35.97% to 40.57% and 20.74% to 30.98% for the 1and 7-month-old leaves powders respectively, fermented at 37℃ and from 35.97% to 39.79% and 20.76% to 23.72% for the 1and 7-month-old leaves powders respectively, fermented at 30℃. There was a negative correlation between pH, total and reducing sugar contents, time as well as fermentation temperature, whereas there was a positive correlation between total protein content and pepsic digestibility of protein and fermentation time. From these results, fermentation of M. oleifera leaf powder by Lactobacillus plantarum A6 increases protein content, pepsic digestibility of protein and availability of iron and reduces the phytates content of these powders.