The present invention is to provide a production technology by which an optically active 2-[6-(hydroxymethyl)-1, 3-dioxan-4-yl]acetic acid derivative, which are of value as pharmaceutical intermediates, can be produced from inexpensive and readily available starting materials without using any extraordinary equipment such as an ultra-low-temperature reactor.The present invention is a production process of an optically active 2-[6-(hydroxymethyl)-1,3-dioxan-4-yl]acetic acid derivative which comprises reacting an enolate, prepared by permitting a base or a 0-valent metal to act on an acetic acid ester derivative with (S)-.beta.-hydroxy-.gamma.-butyrolactone at a temperature not lower than -30.degree. C. to give a dihydroxyoxohexanoic acid derivative, treating the same with an acylating agent in the presence of a base to produce a dihydroxyoxohexanoic acid monoacyl derivative, reducing this compound with a microorganism to produce a trihydroxyhexanoic acid monoacyl derivative, treating this compound with an acetal-forming reagent in the presence of an acid catalyst to produce an acyloxymethyldioxanylacetic acid derivative, and finally, subjecting this compound to solvolysis in the presence of a base.