本研究以台灣企業為研究對象，探討公司融資決策與市場時機之關係。以樣本研究期間內每月份辦理初次公開發行（IPO）家數相對多寡為衡量股市冷熱性之指標，藉由觀察於冷、熱市辦理IPO公司的融資決策差異來分析國內企業是否存在市場擇時行為以及其對資本結構的長短期影響。 實證結果顯示，熱市IPO公司於IPO當年之權益融資幅度明顯多於冷市IPO公司，使其負債比率顯著低於冷市IPO公司，然自IPO後二年起，擇時效果便逐年遞減，顯示擇時行為對資本結構的影響相當短暫，由於不論冷、熱市IPO公司，於IPO後均仍傾向依國內企業偏好之融資順位即先權益後舉債之方式籌資，且IPO後負債比率有逐年回升並趨近於IPO前水平之趨勢，顯示長期而言，國內公司資本結構相當穩定，因此推測國內企業資本結構之決定方式可能為動態抵換理論與融資順位理論之結合，即公司會在可接受之負債比率波動範圍內依照偏好之融資順位進行籌資。由於市場擇時並非調整資本結構時之主要考量，故其對資本結構的影響也相對有限，因此隨時間經過，之前的擇時行為便無法解釋公司後來資本結構之變動。 之前相關實證研究均採用市值對帳面價值比為擇時行為代理變數，本研究於比較不同方法之實證結果後發現，在台灣，市值對帳面價值比除了可作為衡量股市錯價之指標外亦可衡量公司未來成長機會，故若單使用市值對帳面價值比為代理變數將使得實證結果對於市場擇時的解釋力較為薄弱。 / This paper examines the capital structure implications of market timing. I use initial public offering as a single timing event of financing. Market timers would be those firms that go public in hot issue markets. I find that hot-market IPO firms issue more equity and hence their debt ratios decline more than cold-market ones at the end of IPO year. However, the timing effect diminishes with time and in two years after IPO, there is no significant difference between hot and cold-market firms’ debt ratios anymore. After the initial public offering, both firms’ tend to raise capital needs based on their preference financing order, which means retained earnings first, then equity issuance and finally raising debts in Taiwan. In addition, the debt ratios seem to steadily approach to their pre-IPO levels. These all might reveal that, the dynamic trade-off theory and pecking order theory would be better than the market timing theory to explain firms’ capital structures in Taiwan. Some related studies followed Baker and Wurgler（2002）’s approach, using market to book ratio as firms’ market timing proxy. I compare the results of different proxies and find that in Taiwan, market to book ratio could not only be a timing proxy but referring to a firm’s growth opportunity as well. Hence, it should be avoided using market to book ratio as a single proxy of firms’ market timing behavior when studying firms’ capital structures in Taiwan.