The meridian 138° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Pacific Ocean, Australasia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole. The 138th meridian east forms a great circle with the 42nd meridian west. In Australia, the border between the Northern Territory and Queensland approximates the meridian. The border runs north from Poeppel Corner at a bearing of 359° 59' 30", reaching the Gulf of Carpentaria several hundred meters west of the meridian.

From Pole to Pole

Starting at the North Pole and heading south to the South Pole, the 138th meridian east passes through: ! scope="col" width="130" | Co-ordinates ! scope="col" | Country, territory or sea ! scope="col" | Notes ! scope="row" style="background:#b0e0e6;" | Arctic Ocean ! scope="row" | 🇷🇺 ! scope="row" style="background:#b0e0e6;" | Laptev Sea ! scope="row" | 🇷🇺 ! scope="row" style="background:#b0e0e6;" | Sea of Okhotsk ! scope="row" | 🇷🇺 ! scope="row" style="background:#b0e0e6;" | Sea of Okhotsk ! scope="row" | 🇷🇺 ! scope="row" style="background:#b0e0e6;" | Sea of Japan ! scope="row" | 🇯🇵 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" | 🇮🇩 ! scope="row" style="background:#b0e0e6;" | Arafura Sea ! scope="row" | 🇮🇩 ! scope="row" style="background:#b0e0e6;" | Arafura Sea ! scope="row" style="background:#b0e0e6;" | Gulf of Carpentaria ! scope="row" | 🇦🇺 ! scope="row" style="background:#b0e0e6;" | Gulf St Vincent ! scope="row" | 🇦🇺 ! scope="row" style="background:#b0e0e6;" | Indian Ocean ! scope="row" style="background:#b0e0e6;" | Southern Ocean ! scope="row" | Antarctica