The present invention provides a method of producing high-purity hydroxypivalaldehyde and / or
dimer thereof, including: reacting isobutyl
aldehyde with
formaldehyde in a presence of a basic catalyst; distilling a low
boiling point component including unreacted isobutyl
aldehyde to obtain an
aqueous solution; adding a
diluent to the
aqueous solution; cooling the
aqueous solution to crystallize the hydroxypivalaldehyde and / or the
dimer thereof; and subjecting the aqueous solution to a
solid-liquid separation, followed by washing with an
organic solvent and / or water, in which the
diluent and a basic compound are added to the aqueous solution containing the hydroxypivalaldehyde and / or the
dimer thereof obtained by distilling the low
boiling point component off so that a concentration of the hydroxypivalaldehyde and / or the dimer becomes 5 to 23% by
mass, the concentration of
formaldehyde becomes 0.2 to 2.5% by
mass, and a pH value becomes 5.0 or more, the solution is crystallized at a temperature of 20 to 45° C. and subjected to the
solid-liquid separation. In this method, handling of a high-
viscosity slurry and carrying out any complicated operation such as regeneration of an
ion exchange resin are not required, so the high-purity HPA and / or the dimer thereof can be obtained in high yield with an energetically advantageous manner.