Boundary Street (Chinese: 界限街; Cantonese Template:IPA2, Jyutping gaai3 haan6 gaai1; Mandarin Pinyin: Jiè Xiàn Jiê) is a three-lane one-way street in Kowloon, Hong Kong. It runs in the eastbound direction starting at its intersection with Tung Chau Street in the west, and ending at its intersection with Prince Edward Road West in the east, near the former Kai Tak Airport.
Historically, the street marked the boundary between the southern part of Kowloon, ceded by Qing China to the United Kingdom in 1860, and the northern part of Kowloon (New Kowloon), which remained part of China until it was leased as part of the New Territories to the United Kingdom in 1898 for 99 years. After the lease, the boundary was renamed from Boundary Line to Old Frontier Line.
Although the street is the historical mark on the boundary, the road did not come to exist until 1934, more than 30 years after the lease of boundary north. The road was built to accelerate the development of Kowloon Tong and identify the difference in calculation of rates between the boundary north and south.
In modern day conversations, however, New Kowloon is often not regarded as part of the New Territories, but as part of the Kowloon urban area (on both sides of Boundary Street).
Administratively it forms part of the boundary between Yau Tsim Mong District and Sham Shui Po District.
On 1 July, 1997, sovereignty of the territories on both sides of Boundary Street was transferred from the United Kingdom to the People's Republic of China, along with the rest of Hong Kong.