In order to gain a better understanding of how surface treatment and particle size influence the performance of Si nanoparticles as anode material in lithium ion batteries, electrochemical performance of Si particles with size ranges of 20–30nm, 30–50nm, 100nm and 1–5μm in statically self-assembled Si/Graphene composites were compared. Silane agent was introduced to the Si surface rendering a positive charge, which subsequently bonded with graphene oxide (GO) possessing negative surface charges. The following reduction resulted in Si/Graphene (Si/G) composites. It was found that the piranha pre-treatment before introduction of silane agent provided more stable cycling performance for all sizes tested. This effect may be attributed to stronger bonding between Si particles and GO that led to more stable Si/graphene structure. The 100nm Si/Graphene samples with piranha treatment demonstrated the highest discharge capacity of 1,561 mAh/g after 100 cycles at a current density of 0.5C. It consistently showed higher discharge capacity compared with the 30–50nm sample and 20–30nm sample at discharge rates ranging from 0.1C to 1C. Meanwhile, 30–50nm sample with piranha treatment demonstrated the highest capacity retention of 80% after 100 cycles at 0.5C.