Shares in Siam Cement Pcl fell 1.2 percent to 337 baht, the lowest since Jan. 27, on expectations the country's biggest industrial conglomerate would report weak profits for the first quarter due to lower petrochemical margins.

The spread between high density polyethylene (HDPE) and naphtha, seen as a key indicator in assessing the company's profitability, fell to $376 a tonne in the first quarter, said broker Asia Plus Securities.

The company's operating profit was expected to fall 39 percent to 5.59 billion baht ($180.56 million) in the quarter, the broker said.

Petrochemical demand for the quarter was hurt by a slowdown in global economy, the broker said. It still advised investors to buy the stock for long term investment, with target price of 425 baht.

"Despite the short term impact of weak first quarter earnings, we think it's still good for long term investment due to solid business strategy," the broker said.

Siam Cement shares had risen 8 percent this year, underperforming the broader market's gain of 12.6 percent.

1235 (0535 GMT)

(Reporting by Viparat Jantraprap in Bangkok; viparat.jantraprapaweth@thomsonreuters.com)