Leiyang (simplified Chinese: 耒阳; traditional Chinese: 耒陽; pinyin: Lěiyáng) is a county-level city and the third most populous county-level division in Hunan Province, China. Leiyang is under the administration of the prefecture-level city of Hengyang. Located on the south of the province, the city is bordered to the north by Hengnan County, to the west by Changning City, to the south by Guiyang and Yongxing counties, and to the east by Anren County. Leiyang City covers 2,656 km² (1,025 sq mi) with a registered population of 1,413,913 and resident population of 1,150,241 (as of the 2010 census). The city has six subdistricts, 19 towns and five townships under its jurisdiction. The government seat is Caizichi Subdistrict.

Leiyang is the hometown of Cai Lun, the inventor of papermaking technology, one of the Four Great Inventions. It has more than 2,000 years of history as an ancient city named after the north of Lei River. Archaeological excavation proved that as early as the Neolithic Age, people have lived in the territory of Leiyang.

Until Leiyang was built as a division, it was a part of Jingzhou, one of the Nine Provinces before the Spring and Autumn period and a part of Chu State in the Warring States period. In the 26th year of the reign of Qin Shi Huang (221 BC), Lei County (Chinese: 耒县) was formed and took its name after the Lei River, it was part of Changsha Commandery. Dividing Changsha Commandery into Changsha State and Guiyang Commandery (Chinese: 桂阳郡; not to be confused with present-day Guiyang County) in 202 BC, Guiyang Commandery was formed from the southern portion of Changsha Commandery, the county of Lei was renamed to Leiyang and part of Guiyang Commandery.

In the Three Kingdoms period (220–280 AD), Leiyang was the territory of the Wu state. In 257 AD, the county of Leiyang was divided into four counties, that the two counties of Xinping (Chinese: 新平县) and Xinning (Chinese: 新宁县) were located on the western side of Chongling River, and the two counties of Leiyang and Liyang (Chinese: 利阳县) on the eastern side of Chongling River and western bank of Lei River. The three counties of Xinping, Xinning and Liyang were located in Xiangdong Commandery (Chinese: 湘东郡) and the county of Leiyang in Guiyang Commandery.

In 395 AD, the county of Liyang was merged to Leiyang. The county of Leiyang was renamed to Leiyin (Chinese: 耒阴县) in 589 and restored the name of Leiyang in 621. In the Five Dynasties and Ten Kingdoms period (907–960 AD), Leiyang was the territory of the Machu State. The county of Leiyang was renamed to Laiyang (Chinese: 来阳县) during the Song dynasty and restored the name during the Yuan dynasty. In November 1986, the county of Leiyang was reorganized as a county-level city.

According to the historical novel Romance of the Three Kingdoms, Pang Tong was chosen as magistrate of Leiyang by Liu Bei. After three years he had failed to fulfill the duties of his office. Many were upset by his failure and appealed to Liu Bei. Liu Bei sent Zhang Fei, his sworn brother, to Leiyang to investigate. Before Zhang Fei arrived, Pang Tong, who knew that Zhang Fei loved wine, ordered that all wine must be diluted with water. Once Zhang Fei arrived, true to his reputation, he consumed copious amounts of wine, but wondered why he never became drunk. He realized what was going on and became very angry with Pang Tong. In order to appease Zhang Fei, Pang Tong agreed to finish the three years worth of backlogged cases within three days, which he did. For this, Pang Tong was promoted by Liu Bei and to honor the occasion, a special wine was created, now known as Zhang Fei Wine.

In 1928, according to the biography of Mao Zedong by Jung Chang and John Halliday, Leiyang, along with neighboring Chenzhou was razed by troops under the command of Zhu De, who was following directives which originated in Moscow and passed on by higher officials of the Chinese Communist Party. The strategy was to leave large numbers of peasants with no option but to join communist uprisings.

Leiyangers speak a dialect resembling Gan Chinese.