South Korea's top 10 business groups saw their profitability drop this year largely due to increased competition and the global economic slowdown, data showed on Thursday.

The combined operating income of 83 firms affiliated with the country's top 10 business groups reached 36.35 trillion won ($34.27 billion) in the first nine months of the year, down 4.7 percent from 38.15 trillion won a year earlier, according to the data compiled by Chaebol.com, which tracks the conglomerates.

Their sales gained 1.9 percent on-year to reach 517.9 trillion won over the cited period, but the ratio of operating income to sales, a key barometer gauging their profitability, declined 0.5 percentage point to 6.9 percent over the cited period, the data showed.

Only two groups -- SK and LG -- saw their profitability improve this year, while Hyundai, POSCO and six other groups suffered a drop in their sales and profitability.

"Following last year, the country's major conglomerates suffered a sharp decline in their profitability," an official at the research firm said. "What makes things worse is that their profitability will not improve sharply next year."

Samsung Group, the country's top business group, logged a 10 percent rise in sales in the first three quarters, and a 2.2 percent gain in operating income. But the group's ratio of operating income to sales suffered a 0.8 percentage point decline to 10.8 percent.

Hyundai Motor Group, the No. 2 conglomerate, also saw its sales and operating income drop 2.2 percent and 9.6 percent, respectively, in the first nine months of the year, with its ratio of operating income to sales falling 0.6 percentage point to 7.4 percent over the cited period, the data showed.

POSCO, the country's top steelmaker, suffered a 13.5 percent drop in its sales through September this year, with its operating income also sinking 29 percent over the cited period, the data showed.

But SK and LG posted a rise in its sales and operating income this year.

SK Group saw its operating income surge 80 percent with its operating income-sales ratio jumping to 9.7 percent from 5.5 percent.

LG Group also enjoyed a 14 percent rise in its operating income with the ratio of operating income to sales rising to 4 percent from 3.6 percent, according to the data. (Yonhap News)