  Distributing quantum state and entanglement between distant nodes is a
crucial task in distributed quantum information processing on large-scale
quantum networks. Quantum network coding provides an alternative solution for
quantum state distribution especially when the bottleneck problems must be
considered and high communication speed is required. Here, we report the first
experimental realization of quantum network coding on the butterfly network.
With the help of prior entanglements shared between senders, two quantum states
can be crossly transmitted perfectly through the butterfly network. We
demonstrate this protocol by employing eight photons generated via spontaneous
parametric down-conversion. We observe cross-transmission of single-photon
states with an average fidelity of $0.9685\pm0.0013$, and that of two-photon
entanglement with an average fidelity of $0.9611\pm0.0061$, both of which are
greater than the theoretical upper bounds without prior entanglement.
