From building scale to metropolitan, urban green areas vary in size and functions. One of these green areas is urban parks, which have environmental, economic and social benefits for the cities. Besides having recreational opportunities for the urban dwellers, they host rich bio-diversity with diverse flora and fauna with respect their size and they contribute to the sustainability of the city. Transformation of old hunting lands to public greens brings out the concept of urban parks. In historical process, the main reason behind the designation of urban park is mostly to improve life quality after the industrial revolution and rapid urbanisation. Urban green areas can also play an important role in sustaining urban water cycle. Designing and planning of urban green areas are critical to improve hydrological cycle and manage the water in site. From 19th century, Olmsted designed urban parks as a part of the urban infrastructure as in Central Park and Emerald Necklace, and he designed the parks to function as the natural drainage and reservoir systems. These two epic urban parks not only bring rural to urban with aesthetical concerns, but also provide the resilience and sustainability for city systems. Today, contemporary urban park designs deal with environmental incidents more than ever because of the rising global ecological challenges. In this paper, how can urban parks contribute to improve urban hydrological systems will be examined through projects from the world.