The stock price usually decrease on the ex-dividend date by an amount roughly equal to the dividend paid. This reflects the decrease in the company's assets resulting from the declaration of the dividend.
--- For example, when a dividend of $1,000,000 is declared (e.g. 6 sen per share), distributed and paid, the corporation’s cash is reduced by $1,000,000 and its retained earnings (part of stockholders’ equity) is reduced by $1,000,000. Due to the reduction in the corporation's cash/equity, it's stock price is also reduced accordingly (as the company's stock price is a reflection of it's assets (which including it's cash). If the stock price was RM 1.50, it would be RM 1.44 (RM 1.50 - 0.06) after the dividend is allocated.
Dividend : 6 sens
Ex-date : 20/5/2009
In-dividend date share price (19/5/2009): RM 1.50
Ex-dividend date share price (20/5/2009): RM 1.50 - 0.06 = RM 1.44