Information on zooplankton abundance is essential to evaluate the health of marine ecosystems. Nevertheless, this field remains poorly studied in many regions. The purpose of this study was to describe the zooplankton seasonal abundance with environmental responses on the northwestern coast of Sado Island, where has no detailed studies. Horizontal zooplankton diversity and environmental responses were examined monthly from April 2022 to January 2023 in 3 sampling stations (St.); St. A located 5 km and St. B 1 km from the coastline and St. C on the coastline. The Zooplankton community comprised 181 OTU. The community structure of zooplankton on the coastline was more diverse from the open sea. Plankton diversity was maximum in autumn whereas abundance peaked in summer in the deepest sampling station (St. A). The calanoid copepods and nauplii were more abundant in spring while radiolarians showed remarkable abundance in summer and autumn. Foraminifera and Appendicularia were also abundant in autumn and winter. Large-size copepods were found in autumn than in other seasons. The abundance of cyclopoids and calyptopis was positively related to DO but Radiolaria, Aulosphaera trigonopa was positively related to temperature. Overall, distinct seasonal changes in zooplankton distribution and abundance on Sado Island were uncovered.