Experiments of planting days for sticky maize variety HN88 were conducted on one-rice-crop land in Gia Sang ward, Thai Nguyen city, Thai Nguyen province. Experiments included 5 planting days: planting day No.1 (sown 9/2), planting day No.2 (sown 19/2), planting day No.3 (sown 1/3) planting day No.4 (sown 11/3), planting day No.5 (sown 21/3). Experimental results showed that: The earlier the seeds was sown, the longer the growing time was, ranged from 90-99 days. The different planting days did not affect on plant height, corncob-made height of HN88
number of leaves, leaf area index of treatments of sooner planting days were higher than the later. Treatments no. 1, 3 and 5 had good falling resistant. HN88 maize variety was lightly infected by insect and diseases on such treatment of planting days. The yield of fresh corn of HN88 in experimental treatments ranged from 8.57 to 13.57 tons/ha, treatment of sowing on 19/2 had the highest yield (13.57 tons/ha), treatment of sowing on 21/3 had the lowest yield (8.57 tons/ha). Yield of stems and leaves decreased through late planting days. Treatment of sowing on 9/2 had the highest yield (stems - leaves) - 3.34 tons/ha, treatment of sowing on 21/3 had the the lowest yield (2.15 tons/ha).