The invention provides a method of manufacturing a water-absorbent resin composition containing water-absorbent resin particles and additive particles, by which it is possible to obtain a water-absorbent resin composition that sufficiently exhibits additional functions, such as an anti-blocking property under moisture absorption, of the additive particles while maintaining an excellent water absorption property. A method of manufacturing a water-absorbent resin composition includes a resin particle preparation step and a mixing step. In the mixing step, water-absorbent resin particles which are prepared in the resin particle preparation step are mixed with additive particles in multiple stages by using a plurality of mixing apparatuses to obtain a water-absorbent resin composition.