Existing studies have identified two opposite investment-returns relations: a negative relation between capital investment and expected stock returns, but a positive relation between R&D investment and expected stock returns. However, explanations of these patterns usually are distinct from each other. This paper provides a new unified explanation of both relations through the channel of financial constraints. I find that both R&D-returns and capital investment-returns relations mainly exist in financially constrained segment and are insignificant in unconstrained firms. The strength of these relations increases with financial constraints status. In the constrained segment, the excess returns of the investment spread portfolios cannot be explained by either characteristic-based benchmark portfolios or existing risk factor models. Furthermore, high capital investment portfolio is less constrained, while high R&D portfolio is more constrained. These results suggest that financial constraints can help reconcile these two opposite investment-returns relations.