Sorghum was one of the potential crops to be developed as a food product due to its promising nutritional content. The challenges of sorghum utilization are the high amount of tannin content and its low digestibility. Processing methods such as fermentation are known to able to reduce the tannin content, increase the nutrient content and digestibility, as well as the sensory score of sorghum flour. The aim of this study was to find out the effect of fermentation duration and starter concentration of Lactobacillus plantarum on its chemical and physical properties of modified sorghum flour. The study used Completely Randomized Factorial Design with two samples replication and three repetitions of analysis. Ash, moisture, soluble protein, reducing sugar, tannin content, viscosity, white color intensity, and granule size were evaluated to assess its properties. The obtained data showed that the application of L. plantarum significantly reduced the moisture, ash, reducing sugar, and tannin content, but raised the soluble protein (p<0.05) of sorghum flour and made starch granules to be coarser. The strongest effect was achieved at the condition of 6% starter concentration and 30 hrs of fermentation. This treatment gave a beneficial effect on sorghum protein digestibility.