In this paper, the seismic behaviour of extended endplate moment connection is analysed using finite element method (FEM). First, an existing test setup is modelled and analysed using ANSYS computer program. The model is validated by comparing the results from the finite element with the experimental ones. Afterwards, by changing the dimensions of members of the connection, their effect on the overall seismic performance of connection is investigated. The results show that by enlarging the column depth and stiffening the connection, the seismic performance is improved and the thickness of endplate should be chosen in a way that its moment capacity is larger than the plastic moment of beam.