Influences of combined supplementation of calcium citrate (Ca-Cit) and calcium carbonate (CaCO3) on the hydroxyapatite/collagen (HAp/Col)-sodium alginate (Na-Alg) paste (HAp/Col paste) were investigated. Supplementation amounts of Ca-Cit and CaCO3 were denoted as Nx, where N is a multiplication number to Ca2+ ion amounts for the equivalent reaction with Na-Alg obtained previously. Combined supplementation of 10x Ca-Cit and 2x CaCO3 improved the anti-washout property at a washout ratio of 2.42 +/- 0.72% and pH maintenance at 7.34 +/- 0.08, these values were better than the best HAp/Col paste using Ca-Cit (5.91 +/- 2.73% washout ratio and 6.72 +/- 0.06 of pH). This is due to coordinate effects of initial washout inhibition by weak but rapid formation of long-range network by citric acid followed by long term anti-washout inhibition by strong but slow network formation by Ca2+ ions. The paste also showed good cytocompatibilty that MG63 cells proliferated with the culture time without any significant difference with the HAp/Col dense bodies. The HAp/Col paste is expected to be utilized in minimally invasive surgery of bone defect. (C)2017 The Ceramic Society of Japan. All rights reserved.