In 2021, UNSCO under the Man and Biosphere (MAB) Programme had recognised Penang Hill Biosphere Reserve (PHBR) as the third Biosphere Reserve in Malaysia listed in the World Network of Biosphere Reserve (WNBR). PHBR with an area of around 12,481 hectares includes few landmarks in Penang which are Penang Hill, Penang National Park, Penang Botanic Gardens, Teluk Bahang Dam, Ayer Itam Dam, 6 permanent forest reserves (Bukit Kerajaan Forest Reserve, Teluk Bahang Forest Reserve, Laksamana Forest Reserve, Penara Hill Forest Reserve, Highlands Forest Reserve and Pantai Acheh Forest Reserve) as well as several water catchment areas on the Penang island.

PHBR serves as a central green lung to Penang Island where sustainable economic activities facilitate conservation efforts and vice versa. It encompasses of three major ecosystems which are terrestrial, marine and coastal. This diverse ecosystem is home to a variety of flora and fauna including the Penang Slipper Orchid, Damar Minyak, Dusky Leaf Monkey, Smooth Otter, sea turtle, dolphin and others.

The PHBR has interesting landscape including primary lowland, hill dipterocarp forests, mangroves, wetlands, coral reefs, turtle nesting beaches and the only meromictic lake in Malaysia. This lake which showcases the non-mixing of seawater and freshwater is among the remaining 5 meromictic lakes in Asia and forms a rare ecosystem which becomes the natural habitat for endangered species, such as the endemic toad Ansonia penangensis. So far, historical records and the latest biodiversity assessment of Penang manage to list about 2456 plant species from 206 which around 20 species are on the IUCN Red List (four species are listed as Critically Endangered).