This paper presents Powerline Physical-layer Network Coding (Powerline-PNC), a powerline communication architecture that employs physical-layer network coding (PNC). As the first work that applies PNC in powerline communication, we show that Powerline-PNC improves the throughput of bidirectional information interchange in the powerline network by 100% at the SNR cost of 3dB. Specifically, we design both the PHY layer and MAC layer for Powerline-PNC to support PNC within the existing powerline communication standards. Extensive simulations show that the proposed Powerline-PNC works well in practical powerline channels.