Rhodobryum giganteum is a rare Chinese traditional medicinal moss species and has special therapy value in heart diseases. In the present study, we successfully induced gametophores and protonemata of R. giganteum in vitro from its new shoots, which were disinfected with 0.1% HgCl₂, for eight minutes. We also tested the factors influencing the growth of its protonemata and found that: (1) modified Knop medium is able to facilitate the elongation of the protonemata in vitro and prolong their growth time in vitro, whereas MS medium is able to facilitate the branching of the protone mata, and the protonemata grew slowly in modified White medium, accompanied by the development of gametophores; (2) cutting of the protonemata increases protonemal proliferation in vitro; (3) 2,4-D facilitates the induction of protonemata from leaves at 0.5 mgl^-1, but inhibits the induction and quickens the aging process of the protonemata at 2.0 mgl^-1.