This thesis examines how John Keats employs imageries of vitality in Lamia to express his opinions of the vitalist debate. This debate, peaked at the period from 1814 to 1819, began with different interpretations of John Hunter’s living principle explaining the origin of life. John Abernethy and William Lawrence were two representative physiologists expressing their opinions of vitality in London’s Royal College of Surgeons. Romantic writers were also interested in concepts of vitality in the dimension of politics and religion, contemplating on the danger of superstition and tyranny. Due to its mysterious nature, vitality became a significant concept linking different aspects in Romantic period. In Keats’s case, I claim that with his medical training Keats transforms scientific knowledge into aesthetic expressions of vitality to present how imagination works. He employs concepts borrowed from mesmerism to reflect on the nature and the effects of imagination, such as how to influence others and generate sensations. His writings show his concerns about the birth of living beings and writing of poetry as parallel process of creation. Emotions play a crucial role in both processes. Lamia serves as a site for presenting various imageries of vitality proposed by physiologists, such as blood and electricity. As a hybrid and transformative creature, Lamia represents Keats’s ideas of vitality, embodying the beauty and mystery of life. This thesis explores how Lamia reconciles his quests for literature and for science, revealing their intricate relations.