Transfer entropy plays an important role in causal inference and causal discovery in time series analysis. As an information-theoretic measure, transfer entropy can detect nonlinear causal structures without any prior model assumptions. The transfer-entropy-based causal analysis scenario thus has a broader range of applications than the model-based methods like Granger causality tests. This study generalizes the definition of transfer entropy to time-parameterized quantum processes. We define a basis-dependent operational measure of one-way information flow through incoherent channels, called quantum transfer entropy. Quantum transfer entropy provides a new characteristic of quantum channels. A nonzero quantum transfer entropy indicates the directed causal influence from the source to the target.