In this paper, we present a new TRSS (threshold ring signature scheme) which depends on the worst-case hardness of a lattice problem. We apply Fiat-Shamir transform to a lattice-based identification scheme to obtain the proposed scheme. The hardness of the identification scheme which is the hybrid combination of two different designs is based on inhomogeneous short integer solution (ISIS) problem. We give security proof for the proposed TRSS. Comparing the proposed TRSS and the others which are quantum secure, the size of key pairs and the length of the signature are nearly same. Therefore, the proposed scheme is an alternative to the threshold ring signature schemes in post-quantum area.