We synthesized size controlled a-Si:H nanoparticles in plasma using a hydrogen gas pulse. An inductively-coupled plasma chamber with RF power (13.56 MHz) was designed for this study. Experiments were performed with various hydrogen pulse ON-times ranging between 0.1 to 0.9 seconds for 1 second periods. The size of the synthesized nanoparticles was measured and analyzed using electron microscopy, Scanning Mobility Particle Sizer (SMPS) and Image J software. We observed that the size of a-Si:H nanoparticles decreased when the hydrogen pulse ON-time was increased. The a-Si:H nanoparticles were found to be spherical in shape and uniform. For hydrogen pulse ON-time greater than 0.3 second, we observed agglomerated particles due to an increase in their concentration. We hope that these particles can be used as an alternative anode material for lithium ion secondary batteries.