This study examined the factors that were associated with longitudinal changes for ten years from 2004 to 2014 in time spent on housework by married couples who had a preschooler as their first-born child. It also sought to figure out how much of such temporal changes were attributable to differences in the means on associated factors as well as to differences in the influence or slope of such factors. A total of 9,668 time diaries from the Korean Time Use Survey were used to analyze the influence of couple's weekly work hours, wife's relative income, couple's education and gender role attitudes on the time spent on housework of husbands and wives. Results from descriptive statistics, regression and decomposition analysis were as follows. First, women decreased, while men increased their time doing housework. Second, weekly work hours of husband and wife were related to their time doing housework in every year surveyed. Third, wife's relative earnings and couple's gender role attitudes affected wife's time doing housework more than husbands', whereas couple's education had stronger effects on husbands than wives. However, such influence was apparent on a certain survey year, and then disappeared in another, or became stronger or weaker longitudinally. Fourth, the temporal decrease in wife's housework time and increase in husband's housework time were attributable to social and cultural changes such as reduced working hours, rising female income, higher educational background, and prevalence of egalitarian gender role attitudes. Findings suggest that the trend in spending time on housework is expected to continue, and provide a timely policy implications to facilitate the change.