In order to explore the influence of allantoin on monospores formation and release of Pyropia chauhanii, we used the wild-type strain (PC-WT) which could release monospore and its induced strain (PC-Y1) which could not release monospore as materials, then different strains blade discs of apical, middle and basal sections were cultured in medium adjusted with different concentration of allantoin. The research results showed that, in 6 days after treatment, the order of the release number of the different parts of each disc was middle>apical>basal; With the increasing of allantoin concentration, the numbers of release monospores of PC-WT strain blade discs showed a trend of increasing first and then decreasing, and 10 mmol/L was the optimal allantoin concentration of promoting monospore release. But allantoin could not promote PC-Y1 release monospore. We used 20 mmol/L allantoin of medium to culture the discs of PC-Y1 blade for 8 days, and single somatic cell was obtained using enzymatic hydrolysis from the discs of different section, and continue culturing in vitro. We found that the percentage of single cells developed into conchocelis was 66.1% in treatment group; and the percentage of single cells developed into conchocelis was only 15.2% in control group. The result showed that allantoin could promote differentiation from somatic cell to germ cell of blade in Pyropia.