The assembly of double-stranded (ds) DNA nanocircles both by hybridization with branched oligodeoxynucleotides (ODNs) and by intercalation was analyzed by atomic force microscopy (AFM). Branched ODNs ligated to single-stranded (ss) gap regions of dsDNA nanocircles led to defined, dumbbell-shaped architectures. ODNs containing an aromatic intercalator yielded oligomeric aggregates.