We introduced a truncated delta-endotoxin gene, cry1Ab of Bacillus thuringiensis which has a specific biological activity against lepidopteran insects into chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura]. The chrysanthemum cultivar ‘Shuho-no-chikara’ was transformed using a disarmed strain of Agrobacterium tumefaciens, LBA4404, carrying a binary vector, pIAbT1 that harboured a cry1Ab gene encoding an insecticidal crystal protein fragment of B. thuringiensis var. kurstaki HD-1. Leaf discs were co-cultured with Agrobacterium and thereafter cultured on the callus induction medium containing G418. A total of 92 shoots were regenerated from 1,760 leaf discs on the regeneration medium (5.2 %). The cry1Ab gene was detected in all the regenerated plantlets by Southern blot analysis. The accumulation of Cry1Ab protein in 20 transformed lines, selected at random, was confirmed by Western blot analysis. The level of accumulation of Cry1Ab protein ranged from 4.5 ng to 40 ng per 50 μg total soluble protein (from 0.009 to 0.08 % of the total protein). Insect bioassay was conducted using tobacco budworm (Helicoverpa armigera) larvae. On the lines showing a high expression of Cry1Ab (more than 32.5 ng per 50 μg of total soluble protein), a significantly higher feeding inhibition and/or growth inhibition of the insects was observed, compared to those on the non-transformed control plants.