Abstract: In this study, 13 xyloglucan endotransglycosylases/hydrolases (XTHs) and 8 expansin (EXPs) were screened from safflower floret transcriptome database. Through correlation analysis between the safflower gene expression profile chip and the corolla development, only 4 XTHs (CtXTH1-4) and 1 EXP (CtEXP1) have positive relevance with corolla elongation (r ≥ 0.60) and were therefore validated by qRT-PCR. The full length of these genes were cloned by RACE. According to the bioinformatic analysis, CtXTH1 correlated with the development of the floret, and the expression pattern analysis indicated that CtXTH1 had accumulated in the floret. The recombinant vector (pMT39-CtXTH1) was constructed for gene transformation. Overexpression of CtXTH1 significantly increased the corolla length (about 5.34% to 10.25%) and corolla weight (about 30.00% to 36.02%) in transgenic safflower. The overexpression lines also showed an increasing tendency in the weight of seeds, average number of corollas per cone and average number of seeds in each cone. Meanwhile, overexpression of CtXTH1 had no significant effect on flavonoids. According to the corolla microstructure, the OVX-line tubular part of floret exhibited a looser and irregular character. These data suggested that CtXTH1 can potentially increase relaxation of the tissues and boost corolla elongation. Our study provides a valuable clue for plant breeding in the future.