Affiliates of South Korea's top 10 business groups saw their presence on the main bourse decline in May from end-2012 amid the protracted economic slowdown, data showed Monday.

The market capitalization of the top 10 conglomerates' listed firms came at 713.1 trillion won ($651 billion) on Thursday, down 2.27 percent from 729.7 trillion won tallied in end-2012, the Korea Exchange (KRX) data showed.

The number accounts for 56.62 percent of the combined market cap of the companies listed on the main bourse, down 1.14 percentage points from 57.76 percent tallied in December 2012, the data added.

Samsung Group, South Korea's top conglomerate, saw its market cap reach 317.7 trillion won on Thursday, remaining almost flat by moving down 0.08 percent over the cited period.

Hyundai Motor Group, the world's fifth-largest automotive firm, saw its market cap reach 117.2 trillion won, plunging 10.7 percent from December 2012, trailed by SK Group with 70.3 trillion won.

Affiliates of South Korean telecom giant KT Corp. saw their market cap advance 11.19 percent to 12.9 trillion won Thursday from end-2012, posting the steepest growth among the top 10 business groups surveyed.

By individual affiliate, shares of CJ CGV Co., the operator of South Korea's largest multiplex cinema chain, posted the biggest growth of 78.8 percent over the cited period, trailed by KTIS Corp. with 65.71 percent.

In contrast, shares of Samsung Engineering Co. and Lotte Chemical Co. plunged 47.25 percent and 35.03 percent over the cited period, respectively, the data added. (Yonhap News)