Abstract: Lodging is one of the major factors affecting yield of maize. To determine the effect of plant growth regulator application dates on lodging-resistance and yield of maize, the foliage of'Demeiya-1'and'Demeiya-2'were sprayed with 400 mg·L^-1 ethephon (ETH), 10 mg·L^-1 kinetin (KT) and fresh water (CK) at the 5-, 7-and 9-leaf stages, respectively. Then stem morphology, mechanical indicators, chemical properties, lodging rates at filling stage and grain yield of maize were determined. The results showed that compared with CK, KT treatment at 5-leaf stage increased internode diameter by 21.11% and internode density by 13.23% in'Demeiya-1'maize variety. Also ETH treatment at 7-leaf stage reduced the total length of basal internode by 14.41%, but then increased internode diameter by 10.70% and internode density by 15.46% in'Demeiya-2'maize variety. ETH treatment at 7-leaf stage increased the break strength of internode by 26.04% and 16.77%, and internode penetration strength by 22.77% and 14.62% respectively in'Demeiya-1'and'Demeiya-2'maize varieties. The contents of hemicellulose, cellulose and lignin in internode of'Demeiya-2'increased by 25.49% under ETH treatment at 9-leaf stage. The effect of ETH on mechanics of maize stalks regulation were better than that of KT, although the two plant growth regulators all reduced lodging rate of both maize cultivars. There was a highly significant positive correlation between internode diameter and break strength (r=0.905^**), but significant or extremely significant negative correlation was noted between lodging rate and chemical compositions contents or internode diameter of internode. KT application at 9-leaf stage significantly increased grain yield of'Demeiya-1'(22.24%) and'Demeiya-2'(19.98%), while ETH treatment had no significant effects on maize yield. Based on the results therefore, KT treatment at 9-leaf stage significantly increased maize yield, but lodging-resistance under ETH treatment at 7-leaf stage was better than that under KT.