The Longest Day in Chang'an (Chinese: 长安十二时辰) is a 2019 Chinese historical suspense drama directed by Cao Dun and written by Paw Studio. The series stars Lei Jiayin and Jackson Yee. It is based on the novel of the same name by Ma Boyong. The Longest Day in Chang'an is produced jointly by Youku, Beijing Weying Technology Co., Ltd, Liu Bai Entertainment and Yuyue Film Co., Ltd. The series follows the characters Zhang Xiaojing and Li Bi, and their efforts to foil a terrorist attack on Chang'an, the capital of the Tang dynasty (618–907). It began airing in China on Youku from June 27, 2019.