Provided are: a water-absorbing resin manufacturing method by which it is possible, with respect to water-absorbing resins used in sanitary materials, to obtain a water-absorbing resin that has an appropriate BET specific surface area and water absorption rate the water-absorbing resin a water-absorbing agent formed using the water-absorbing resin and an absorbent article. In this water-absorbing resin manufacturing method, when reverse phase suspension polymerisation involving two or more stages is performed on a water soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium in the presence of at least an azo compound, a peroxide, and an internal crosslinking agent, the BET specific surface area of secondary particles is controlled, said secondary particles being formed by aggregation of primary particles obtained by polymerising by adjusting the usage amount of the internal crosslinking agent during first-stage polymerisation to be within the range 0.015-0.150 millimoles per 1 mole of the water soluble ethylenically unsaturated monomer used during the first-stage polymerisation.關於衛生材料所使用的吸水性樹脂,本發明提供一種吸水性樹脂的製造方法、以及該吸水性樹脂和使用該吸水性樹脂而成的吸水劑、吸水性物品,該製造方法能夠獲得具有適度的BET比表面積和吸水速度的吸水性樹脂。在本發明的吸水性樹脂的製造方法中,是在烴分散介質中,於至少偶氮系化合物、過氧化物及內部交聯劑的存在下,對水溶性乙烯性不飽和單體實行2階段以上的反相懸浮聚合,此時,相對於在第1階段聚合時所使用的水溶性乙烯性不飽和單體每1莫耳,在0.015~0.150毫莫耳的範圍內,調整在第1階段聚合時的內部交聯劑的使用量來實行聚合,藉此來控制由所獲得的一次粒子凝集而形成的二次粒子的BET比表面積。
