Phu Vinh reservoir is an important water resource for drinking water supply and irrigation in Dong Hoi city, Quang Binh province. However, the water bloom of Microcystis is threatening its water quality. This paper aims to identify Microcystis morphospecies occurring in Phu Vinh reservoir and determine microcystins that were produced by Microcystis strains isolated from this reservoir. The results showed that the morphospecies composition of Microcystis in Phu Vinh reservoir consists of M. aeruginosa, M. ichthyoblabe, M. novacekii, M. panniformis, M. pseudofilamentosa, M. ramosa and M. wesenbergii. Of them, M. aeruginosa and M. ichthyoblabe are the main factors causing the water bloom. The study also indicated that Microcystis population in Phu Vinh reservoir can produce microcystin-RR, microcystin-LR, demethyl microcystin-RR and demethyl microcystin-LR.