The prevalent family structure in Korea is shifting from four-member to two-member households, according to the latest statistics. Experts attribute the trend to a dwindling number of households where two generations live under the same roof and an increasing number of married couples who put off having children.

According to Statistics Korea on Thursday, Korea's 4.21 million two-member households accounted for 24.3 percent of the total 17.34 million households as of November last year, the largest portion.

Two-member households made up only 13.8 percent in 1990. In contrast, the ratio of four-member households, which was the most prevalent in 1990, fell to 22.5 percent or 3.9 million households last year.

Among Koreans aged 60-69, two-member households accounted for 39.6 percent and among people over 70 for 40.9 percent. This trend was attributable to the aging society and a growing number of senior citizens who live apart from their children.

Remarkably, two-member households were more prevalent in rural areas and small towns. Among the seven largest cities of Seoul, Busan, Daegu, Incheon, Gwangju, Daejeon and Ulsan, the southern port city of Busan had the largest proportion. But they were the biggest group in seven out of nine provinces, except Gyeonggi and North Chungcheong.

The number of single households is also growing. Last year, there were 4.14 million, up 30 percent from 2005 and taking up 23.9 percent of all households, compared to 20 percent in 2005. 

People in their 20s made up the largest proportion of single households or 21.4 percent in 2005, but last year elderly people over 70 came first with 19.2 percent.

"Income disparity will worsen among one-member and two-member households, which means social security benefits will have to make up for the support previously given by other family members," said Yoo Kyung-joon of the Korea Development Institute.