AbstractAn undirected graph $G$ is determined by its $T$-gain spectrum (DTS) if every $T$-gain graph cospectral to $G$ is switching equivalent to $G$. We show that the complete graph $K_{n}$ and the graph $K_{n}-e$ obtained by deleting an edge from $K_{n}$ are DTS, the star $K_{1,n}$ is DTS if and only if $n\leq 2$, and an odd path $P_{2m+1}$ is not DTS if $m\geq 2$. We give an operation for constructing cospectral $T$-gain graphs and apply it to show that a tree of arbitrary order (at least $5$) is not DTS.