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The exact role of lithium ions (Li+) in controlling alkali–silica reaction is still unclear. Thus, the effects of Li+ on the reaction between reactive silica (quartz glass) and hydroxyl in alkaline solution with or without Ca were investigated by quartz glass powder or slice immersion experiments. When quartz glass was immersed in lithium-containing alkaline solutions, only Li2SiO3 was produced with the absence of Ca, but Li2SiO3 and calcium silicate hydrate (CSH) were formed with the presence of Ca. The quartz glass slice immersion experiment indicated that the mass loss of quartz slices was less than 1% only when Ca was present in the lithium-containing alkaline solution. This was because a dense, low-porosity and strongly bonded production layer mainly composed of CSH and Li2SiO3 crystals was formed on the glass surface and served as a barrier against the diffusion of OH− and alkali ions to the substrate glass.