In this paper we study the residual spectrum of the quasi-split unitary group $G=U(n,n)$ defined over a number field $F$, coming from the Borel subgroups, $L_{dis}^2(G(F)backslash G(Bbb A))_T$. Due to lack of information on the local results, that is, the image of the local intertwining operators of the principal series, our results are incomplete. However, we describe a conjec...