A basic ecological research of the seahorse populations has not been done to date even though the population is declining due to overfishing, by-catching and heavy human activities. Recently reported seahorse (Hippocampus haema) samples were monthly collected in Geoje–Hansan bay for a year from August 2015 to August 2016. Standard length (SL), weight (Wt), coronet height (CH), trunk length (TrL), and tail length (TaL) of each individual were measured for identifying characteristics of H. haema. The ranges of temperature and salinity were 8.2-26.0 °C and 29.3-34.1 ‰, respectively. Mean SL and Wt for all the groups were 55.26 ± 16.11 mm and 0.32 ± 0.25 g, respectively. There were significant differences in the relative ratios of each length factor (TrL, TaL and CH) and condition factors (CFs) according to gender or breeding period (ANOVA, p<0.01). Since pregnant males constituted nearly 40 % (18 individuals) in May and juvenile seahorses were first observed in June, 2016, the recruitment of this species appears to begin in June. Based on our one-year field observation, the duration of the breeding season of the H. haema in Geoje-Hansan bay can be estimated for approximately 7 months long which is similar to other seahorse species (generally 4 to 10 months) inhabiting similar latitudes. The results from this study provide important information for a sustainable management and conservation of the new recorded seahorse species.