Rapid progresses have been achieved in the photonic applications of two-dimensional materials such as graphene, transition metal dichalcogenides, and topological insulators. The strong light−matter interactions and large optical nonlinearities in these atomically thin layered materials make them promising saturable absorbers for pulsed laser applications. Either Q-switching or mode-locking pulses with particular output characteristics can be achieved by using different saturable absorbers. However, it remains still very challenging to produce saturable absorbers with tunable optical properties, in particular, carrier dynamics, saturation intensity as well as modulation depth, to suit for self-starting, high energy or ultrafast pulse laser generation. Here we report a new type of saturable absorber which is a van der Waals heterostructure consisting of graphene and Bi2Te3. The synergetic integration of these two materials by epitaxial growth affords tunable optical properties, that is, both the photocarrier dynamics and the nonlinear optical modulation are variable by tuning the coverage of Bi2Te3 on graphene. We further fabricated graphene−Bi2Te3 saturable absorbers and incorporated them into a 1.5 μm fiber laser to demonstrate both Q-switching and mode-locking pulse generation. This work provides a new insight for tailoring two-dimensional heterostructures so as to develop desired photonic applications.