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Paper is extremely versatile because it is light, inexpensive, biodegradable, and recyclable product. However, it is very sensitive to water. Hence many synthetic resins, that is polyethylene and polylactic acid are often used as barrier coating materials in order to block water absorption into paper. However, the resins are harmful to the environment because they cannot be biodegradable and repulpable. Gas grafting based on chromatogeny chemistry is an alternative to synthetic resins. Hydrophilic surface of fiber can be changed into hydrophobic characteristics by gas grafting. Mechanism of the grafting can be explained as hetergeneous esterification between carboxylic groups in fatty acid chloride and hydroxyl groups in cellulose. In this study, parameters for gas grafting of recovered papers including ONP (old newspaper), OMG (old magazine), and white ledger were investigated. Basically hydrophobicity of ONP was lower than that of OMG and white ledger after flotation. However hydrophobicity of ONP was improved by hyperwashing. From the results, ERIC value gives great influence on efficiency of gas grafting. The esterification could be hampered by residual ink. Calendering gave positive effect to efficiency of gas grafting. Cobb value decreased with increase in sheet density by calendering. Also, hydrophobicity of ONP was improved by acetone washing and repeat of gas grafting. Consequently, residual ink, calendering, and acetone washing followed by repeat of gas grafting were important influencing factors of gas grafting by fatty acid chloride.