Methods of promoting the germination of immature seeds in Lilium japonicum Thunb. at various stages of their development were investigated. 1. Although seeds and embryos reached their final sizes 2 months after pollination, they were immature but 80% of them germinated one month later. 2. The germination rate of immature seeds, harvested 3 months after pollination, then exposed to 30°C for 50 days, and then cooled to 15°C for 30 days were unaffected, whereas it increased one month later. 3. The germination rate of immature seeds, 3 months after pollination, improved significantly after 1) removing the seed coat ; 2) scarification ; 3) soaking in NaOH ; and 4) treatment with NaClO.