Quantitative and morphological characteristics of Phyllospadix iwatensis was investigated seasonally from 2014 to 2016. P. iwatensis was distributed in Hakampo, Gureumpo, Mohang and Tonggae in Taeanhaean National Park. The most average density of P. iwatensis were found at Hakampo (7,063 ± 802 shoots m-2), Mohang (6,583 ± 695 shoots m-2), Gureumpo (6,480 ± 581 shoots m-2), while the fewest were found at Tonggae (5,664 ± 561 shoots m-2). Morphological characteristics of P. iwatensis were different depending on the region and season. To examine the effect of oil pollution, annual variations of seagrasses was compared before the oil spill in 2007 with after oil spill from 2008 to 2014. The density and morphological characteristics of P. iwatensis, which is increasing in spring and summer, decreasing in autumn, suggesting that they have been recovered damages due to the oil spill. Quantitative variation is interpretation by the impact of seasonal fluctuation than the oil spill. In conclusion, the seagresses has received a temporary effect but rapidly recovered. Seagrasses have been recovered from the effect of the oil spill and are playing a significant role ecologically. However shince the seasonally variations of seagrasses fluctuated between years, they probably have not completely recovered. Therefore, the continuous long-term monitoring of seagrass meadows in Taean is required and provides appropriate and fundamental information for restoration of damaged seagrass ecosystem due to the oil spill in Taean.