Foreign investment has great contribution to the economic development of the host countries; however, accompanied with the flow of capital are the risks of environment pollution and resource degradation. While international investment agreements (IIAs) aim to protect economic interests by promoting and encouraging investment, the question arises as to the role of noncommercial values such as environment in IIAs. The article examines the possible conflicts between measures to protect the environment implemented by host States with their obligations of investment protection under IIAs and how such conflicts are resolved under IIAs concerning Vietnam. Through the survey of 66 bilateral investment treaties and several treaties with investment provisions which Vietnam has negotiated and/or participated in since 1990s, the study reveals the emerging trend of integrating environmental concerns into investment treaty-making practices, using a variety of environment languages in the preamble as well as in the text of IIAs. Accordingly, it provides some thoughts and recommendations for Vietnam in drafting and negotiating IIAs toward a more sustainable investment policy.