To figure out the trends of multiple birth rate and to estimate the age specific multiple birth rate, we analyzed population based data (birth certificated data of Korea National Statistical Office) of 633,205 births in 1998 and 469,348 births in 2010 among women giving birth aged 15-49 years. Between 1998 and 2010, multiple birch rate among women aged 15-49 years increased from 1.5 percent to 2.7 percent. In age distribution of women giving birch, women aged 30 and over in 1998 accounted for about 29 percent of all births (singletons & twins/+), and 64 percent in 2010. If age distribution of women giving birth had not changed (the age distribution of birth in 2010 was similar to that in 1998), the age adjusted multiple birth rate would be only 2.3 percent (14.8 percent lower). Multiple birth rates have risen with advancing maternal age, peaking at 35-39 years (2.5 percent in 1998, and 3.8 percent in 2010) and declining thereafter. Multiple birth rates increased for women of all ages (15-49 years) during 1998-2010, with the largest increases among women aged 30-34 (odds ratio: 1.60). The rates increased 1.56 (OR) for women aged 30-34, followed by women aged 35-39 (OR: 1.52), aged 40-49 (OR: 1.47), and aged 15-24 (OR: 1.22).