The aim of this study is to investigate the impact of foreign exchange reserves accumulation on the investment of companies in Vietnam. A detailed data of 332 firms listed on Hochiminh Stock Exchange is collected over the period from the first quarter of 2009 to the first quarter of 2019. Generalized Method of Moments (GMM) is employed to test the proposed hypotheses in this study. Estimation results reveal that great changes in foreign exchange reserves reduce corporate investment. Besides that, according to the growth stage of reserve accumulation, to some extent, foreign exchange reserve accumulation benefits domestic investment. However, when reserves increases tremendously, it may cause negative effect to investment. The study also investigates the impact of foreign exchange reserves on investment of companies in different industries. Empirical findings point out that for firms which are newly listed, young, small, and has low investment in fixed asset and low dividend payout ratio, the investment-cash flow sensitivity is very high. Changing in foreign exchange reserves does not greatly affect firm investment. In contrast, for enterprises which are long-established, large, and has high fixed asset value and high dividend payout ratio, the investment-cash flow sensitivity is lower. However, large change in the accumulation of reserves adversely affects firm investment. The empirical findings imply that government should be more cautious in managing foreign exchange reserves and firms should develop a plan to effectively manage their cash in order to lower borrowing costs as well as to less depend on external financing sources.