Switchgrass (Panicum virgatum L.) is one of the most important crops for forage and bioenergy, and embryogenic callus is an important material for molecular breeding of this species. In this study, the longevity of caryopsis-derived compact Type I callus of switchgrass was investigated during 24 months. The regeneration ability of the callus was gradually reduced after 18 months of subculture, but remained at a relatively high level after 24 months. In addition, albino formation was not induced throughout the 24-month subculture. Casamino acids improved the regeneration ability of embryogenic calli without apparent morphological change or albino induction, while proline induced friable Type II calli as well as albino shoots. Cell straining treatment coupled with medium containing casamino acids led to 4-fold higher regeneration ability. The ploidy levels of 24-month-old calli were similar to seedling explants. The present results indicate that caryopsis-derived Type I callus is stable and could be maintained long-term, and thus would be a useful source for genetic transformation of switchgrass.