Atomic layer deposition (ALD) was used to deposit TiO2 on the surface of vitamin C powder to enhance its medicinal stability. Coating of TiO2 on vitamin C was carried out through four consequent steps in each cycle: (i) N-2 purge, (ii) TiCl4 pulse injection, (iii) N-2 purge, and (iv) H2O pulse injection. Effects of TiCl4 injection time, hydrodynamic regime of fluidization and reactor temperature were investigated on the ALD process. Effect of TiCl4 injection time on the surface saturation of vitamin C by Ti at different times was investigated. Amount of TiO2 deposited on the surface of vitamin C remained almost unchanged for injection times between 20sec and 120sec while it increased significantly when this time was increased to 300sec. Particle erosion and increase of the available surface area were the reason for this trend. It was also shown that by changing the flow pattern from fixed bed to bubbling and then to turbulent fluidization, TiO2 content on vitamin C was increased due to enhancement of mixing. It was found that TiO2 deposition on vitamin C was decreased by increasing temperature. Medicinal stability tests showed that the stability of vitamin C increased by increasing the TiO2 load on vitamin C.