Two genetically unrelated normal dent maize inbreds, ICI63 and ICI92, with different heterotic backgrounds were used for studying environmental temperature effects on grain yield and quality. These two maize inbreds are used in commercially available hybrids and are proprietary to ICI Seeds. The maize inbreds were grown in a greenhouse to control the growing condition of the plants. After 14 days post-pollination, the ears were wrapped in temperature control devices set at 25 or 35∘ C during the grain-filling period. Grain yield, kernel weight, and kernel density were less for ears developing at 35∘ C than for those at 25∘ C. The extent of the reduction, however, was different for each variety: 13.1 and 37.9% less kernel weight and 8.47 and 10.08% less density for ICI63 and ICI92, respectively. At the increased temperature, starch granule size decreased, and gelatinization onset temperature increased. The starch granules of ICI63 became more oval-shaped when the developing temperature was set at 35∘ C, but there was no change in shape for ICI92. At the higher developmental temperature, amylose content of ICI63 and ICI92, determined by iodine affinity, decreased 2.39 and 2.20%, respectively. Amylose molecular weight of both varieties also decreased. Size-exclusion chromatography and high-performance anion exchange chromatography revealed an increased medium branch-chain fraction and decreased long and short branch-chain fractions for ICI63 amylopectin, whereas amylopectin from ICI92 possessed increased long and medium branch-chain fractions and a decreased short branch-chain fraction when developed at 35∘ C. An in vitro model study, in which a 3.5 mg/mL water dispersed amylose solution was used, was performed to determine the effects of temperature on conformation and properties of amylose molecules in aqueous solution. The retrogradation rate, an index of association and double helix formation in amylose molecules, decreased as incubation temperature increased. The initial retrogradation rate decreased from 58.8 to 17.4% after one day when the temperature was increased from 5 to 15∘ C. The rate further decreased with a significantly smaller discrepancy to 12.5, 9.2 and 7.1% after one day at 25, 35 and 45∘ C, respectively. As incubation temperature increased from 5 to 45∘ C, number- and weight-average degree of polymerization of double helix segments of retrograded amylose increased from 39 to 52 and 47 to 72, respectively. This study demonstrated that environmental temperature has an effect on the maize starch fine structure. In addition to temperature effects on starch synthesis enzymes, the simple physical phenomenon of growth temperature can directly affect the conformation of starch molecules.