Abstract: In this paper, the photopeirod sensitivity of 6 corn varieties was measured. Six corn varieties are male and female parents plants of Huanong No. 1, F1 generation hybrid, F2 generation hybrid and other two contrastive varieties. The effects of long-day photoperiod on plant growth were done in Inner Mongolia by pot culture. The results indicated that significant difference of photoperiod sensitivity was observed among 6 varieties. Based on the index of total leaf number (TLN), those varieties could be divided into four types: the extremely sensitive type, sensitive type, relatively sensitive type and relatively non-sensitive type. The results in pot culture experiment showed that the photoperiod significantly regulated shoot growth of the sensitive type, but had no significant effects on the relatively non-sensitive type. Under the conditions of long-day light in Inner Mongolia, the numbers of plant height, shoot dry mass, stem girth of sensitive ensilage corn were low in seedling stage (5-leaf period), but significantly increased in harvest stage. Being long-day light inhibition, the extremely sensitive type grew relatively slowly in all of its development stages. The results also indicated that photoperiod sensitivity appeared in F1 generation and separated in F2 generation.