The number of newborn babies came in at 25,236 in July, down 1,770, or 6.5 percent, from a year earlier, according to Statistics Korea. It was the lowest July figure since statistical office began compiling the data in 1981.
For the first seven months of this year, the childbirth was 183,787, down 7.6 percent compared with the same period of last year.
The country's newborns continued to fall amid the growing social trend of delayed marriage and the sliding number of women who are of childbearing age.
The number of marriages declined 4.5 percent from a year earlier to 19,180 in July, staying slightly above the record low of 18,964 tallied in July 2017.
The continued slide in childbirth fueled concerns about the demographic cliff, which refers to a sudden drop in the heads of household eventually leading to a consumption cliff.
The low birth rate has been a headache for the South Korean economy as it can lead to the lower workforce amid the rapidly aging population, which could drag down the economy's growth potential.
Meanwhile, the number of divorces grew 1.8 percent over the year to 9,497 in July, while the number of deaths fell 3.0 percent to 23,172 in the month.