本研究主要探討當公司管理階層選擇自願性會計政策變更時，是否影響市場對於各該公司所發布相關訊息的反應情形，進而造成股價持續波動之狀況。本研究亦探討是否會計政策的異質性(公司進行會計變更後採用與其同業不同的會計政策)會影響到前述自願性會計變更與股價反映之關係。本研究以採用自願性會計政策變更之美國上市公司為研究對象，樣本期間為1994年至2008年，並將研究對象之競爭對手或產業領導者納入比較樣本。此外，為了觀察股價持續反應的情況，我們設立了季報發布期間和季報發布後期間，以檢驗此研究之假說。 此研究結果顯示，整體來說，自願性會計政策變更在季報發布期間對於未預期盈餘和報酬的關係，會有顯著正向之關聯。此外，考慮了會計政策之異質性後，若公司在會計變更後採取了與同業相同之會計政策，在季報發佈期間對於未預期盈餘和報酬的關係會有顯著正向之關聯，而在季報發佈後期間對於未預期盈餘和報酬的關係會有顯著負向之關聯；若公司在會計變更後採取了與同業不同之會計政策，市場在季報發布後期間對於未預期盈餘和報酬的關係會有顯著正向之關聯，比較多的資訊反映於季報發佈後期間。所以，當公司會計變更後採取異質性的會計政策，外部使用者對於公司發布之相關資訊可能無法及時的消化和理解，進而導致市場遞延反應。 因此，雖然公司採用自願性會計政策變更可能是為了要更真實反映公司之營運狀況，提升外部人士對於公司的實質了解，但根據本研究的實證結果顯示，外部使用者對於自願性會計政策變更後之相關訊息可能需要比較長時間的理解，導致股價會有持續反應的情況。 / This study investigates the relation between voluntary accounting changes (VACs) and post-earnings announcement drift. In addition, this study examines how accounting choice heterogeneity (different from the VAC firms’ peers) before and after VACs is associated with such association. This study collects VAC firms in the U.S. among 1994 to 2008 and identifies the heterogeneity of accounting choices between VAC and non-VAC firms. To test the hypotheses, this study considers the 10-Q filing window and a post-filing drift window. The results demonstrate that, overall, VACs have a positive effect on the three-day market reactions to 10-Q filings. In addition, after taking into account the accounting choice heterogeneity, this study observes that more of earnings-related stock price reaction occurs in the 10-Q filing window and less of earnings-related market reaction appears in the post-filing drift window. Moreover, VACs are positively associated with the post-filing period drift when VACs are different from their industry peers after VACs. That is, VAC firms adopting different post-change accounting method from non-VAC firms may make external users harder to digest related earnings information and lead to delayed market reaction, thus, more of stock price drift occur in post-filing window. In conclusion, though VACs may enhance market participants’ understanding of firms’ activities, the results demonstrate that market participants may spend more time to comprehend and digest VAC information disclosed by VAC firms compared to non-VAC firms, which leads to post-earnings announcement drift.