1-(4-Alkylphenyl)-3-hydroxy-2-methyl-4-pyridones (AHMP or HL) having 1 to 12 carbon atoms in their alkyl chains were synthesized and used for the extraction of indium(III) from aqueous solutions into 1,2-dichloroethane. The extracted species were InL3for all AHMP. The partition coefficients, KDof AHMP and the distribution constants, KDCof indium(III)-AHMP complexes increased with an increase in the carbon number in the alkyl chain. The increments of log KDand log KDCwere 0.52 and 1.67 per a carbon atom, respectively. The proton dissociation constants of AHMP and the extraction constants and the formation constants of their indium(III) complexes were also determined.