Background To investigate the expression of elastin in the conjoint facial sheath (CFS) in patients with severe unilateral congenital blepharoptosis in different age groups. Methods Twenty-seven cases of severe unilateral congenital blepharoptosis (27 eyes) were treated with CFS + LM complex suspension from January 2020 to July 2020. Within that sample, 9 patients were over 18 years old, 9 patients were 13 to 17 years old and 9 patients were 5 to 12 years old. CFS and LM specimens were collected during CFS + LM complex suspension surgery. In the CFS specimens, the elastic fibers were observed by Victoria Blue staining. The elastin expression levels of the three groups of specimens were determined and analyzed by immunofluorescent staining and Western blotting. Results Victoria Blue staining showed that elastic fibers were abundant in CFS tissue. Moreover, immunofluorescent staining showed strong positive expression of elastin in the CFS and LM. Furthermore, in the child group, the Western blot results demonstrated that the expression of elastin was higher in the CFS than in the LM (P < 0.05). Additionally, the expression of elastin was significantly higher in the CFS of children than in that of adults or adolescents (P < 0.001). Conclusions The CFS and LM are rich in elastic fibers and elastin, although elastin expression in the CFS decreases with age. Thus, it is feasible to apply CFS + LM complex suspension to cure severe unilateral congenital blepharoptosis.