Abstract. We show that partial 2-tree canonization, and hence isomorphism testing for partial 2-trees, is in deterministic logspace. Our algorithm involves two steps: (a) We exploit the "tree of cycles" property of biconnected partial 2-trees to canonize them in logspace. (b) We analyze Lindell's tree canonization algorithm and show that canonizing general partial 2-trees is also in logspace, using the algorithm to canonize biconnected partial 2-trees.