•Cycloamylose (CA) was prepared by combined treatment of isoamylase and TA 4αGTase.•The maximum yield of CA increased from 24.6% to 45.6% after debranching of amylomaize.•The minimum DP of CA produced by TA 4αGTase was 5 despite reaction conditions.•The larger CA molecules (DP > 22) were main constitutes after 24 h of reaction.Amylomaize (AMM) was utilized as the substrate for cycloamylose (CA) production in this study. After debranching, AMM was incubated with 10 U/g of Thermus aquaticus 4-α-glucanotransferase (TA 4αGTase) for various reaction times in water or in DMSO reaction system. The maximum conversion yield of CA was greatly improved from 24.55% to 45.58% and from 27.40% to 47.25% after debranching in the water and DMSO reaction systems, respectively. Compared with the method that produced CA from commercial potato amylose, this method produced CA from a natural amylopectin containing starch with enhanced conversion yield after debranching. Meanwhile, we found that the minimum degree of polymerization (DP) of CA from TA 4αGTase treatment was 5, regardless of the reaction conditions. These results were different from those reported in the literature that stated the minimum DP of CA produced with a TA 4αGTase treatment was 22 regardless of the reaction conditions.