S.Korean stocks end lower on profit-taking in heavyweight firms

* KOSPI falls, foreigners net sellers

* Korean won weakens against U.S. dollar

* South Korea benchmark bond yield rises

* For the midday report, please click

SEOUL, April 28 (Reuters) - Round-up of South Korean financial markets:

** South Korean shares closed lower on Wednesday, marking their steepest fall in a week, as both institutional and foreign investors net sold heavyweight stocks ahead of an expected change in policy on short-selling ban in May.

** The Korean won weakened, while the benchmark bond yield rose.

** The benchmark KOSPI fell 33.95 points, or 1.06%, to 3,181.47 by 0632 GMT.

** Regulators are set to lift the current ban on short-selling of stocks in May, and investors are taking profits now before volatilities increase further, says Lee Won, an analyst at Bookook Securities.

** Among the heavyweights, technology giant Samsung Electronics fell 0.97% and peer SK Hynix slid 3.70%, while LG Chem fell and Naver fell 0.11% and 1.71%, respectively.

** Foreigners were net sellers of 608.1 billion won ($546.27 million) worth of shares on the main board.

** The won was quoted at 1,113.0 per dollar on the onshore settlement platform, down 0.23%.

** In offshore trading, the won was quoted at 1,112.6 per dollar, up 0.1%, while in non-deliverable forward trading, its one-month contract was quoted at 1,112.2.

** The KOSPI has risen 10.72% so far this year, and gained 4.8% in the previous 30 trading sessions.

** The trading volume was 1,397.89 million shares. Of the total traded issues of 908, the number of advancing shares was 189.

** The won has lost 2.4% against the dollar so far this year.

** In money and debt markets, June futures on three-year treasury bonds fell 0.05 point to 110.89.

** The most liquid 3-year Korean treasury bond yield rose by 1.1 basis points to 1.108%, while the benchmark 10-year yield rose by 1.3 basis points to 2.084%. ($1 = 1,113.1900 won) (Reporting by Cynthia Kim; editing by Uttaresh.V)