In this article, we suggest optimizing packet length for two way relaying with energy harvesting. In the first transmission phase, two source nodes N1 and N2 are transmitting data to each others through a selected relay R. In the second phase, the selected relay will amplify the sum of the signals received signals from N1 and N2. The selected relay amplifies the received signals using the harvested energy from Radio Frequency (RF) signals transmitted by nodes N1 and N2. Finally, N1 will remove, from the relay's signal, its own signal to be able to decode the symbol of N2. Similarly, N2 will remove, from the relay's signal, its own signal to be able to decode the symbol of N1. We derive the outage probability, packet error probability and throughput at N1 and N2. We also optimize packet length to maximize the throughput at N1 or N2. © 2019, Academy and Industry Research Collaboration Center (AIRCC).