The Reamker, which has been enormously influential in all aspects of Cambodian arts and culture, is the Cambodian version of the Indian Ramayana epic. Evidences from inscriptions and iconography show that this epic has existed in Cambodia since the 7th century. However, the oldest surviving Reamker text, which is incomplete and composed of two compositions is said to have been written between the 16th and 18th centuries. When the Temple of the Emerald Buddha was built in the Royal Palace in Phnom Penh in 1895, the story of Reamker was selected to be painted on the galleries of the temple and became the only complete version of Reamker in the country. This thesis attempts to explore the sources of inspiration of the Reamker Mural Painting by comparing the Reamker Mural Painting and the Ramakien Mural Painting in the Grand Palace of Thailand in terms of the story, the compositional organization of painting, and the iconography. In addition, the thesis also analyzes the key factors related to similarities and differences found from the comparison. The results show that the Reamker Mural Painting’s episodes were composed from Ramkien Mural Painting in the Thai Grand Palace, the Thai Ramakien text by King Rama I, the Reamker I and II texts, the segment of Reamker text called “Kal Vaiyarab(n) Santam Yak Brah Rama Pan,” and the Reamker oral versions. Although, the painted episodes were adopted from the Thai Palace Mural, the presentations in the painting are completely different. Most of characters in the Cambodian Palace Mural are identical with the Thai Palace Mural, but important differences can also be found. The distinctions came from three key factors: the mistakes were created by the muralists when the painting was transferred between one culture to another; the depictions of characters without ascribing them names; the socio-cultural inspiration and individual context and style. The findings also indicate that the architecture was inspired by the buildings in Cambodia itself rather than from the Thai Palace Mural. The landscapes were adopted from other paintings, not from the Thai Palace Mural. The compositional organization, on the other hand, reflects typical Cambodian characteristics. The main factor for the Thai influences on the Reamker Mural Painting lie in the three key persons responsible for the construction of the Temple and the creation of the mural painting. King Norodom who built the temple, Ukna Tep Nimit Mak who was the chief painter and architect in cooperation with Venerable Nil Teang who was the supervisor of the temple’s construction were brought up and/or studied in Bangkok for many years. This is one of the key trends of Thai influence on Cambodia during the restoration time after the ‘dark age’. The Thai influence is detectable in other arts and culture of this period, namely, Buddhist religion, literature, dance drama, music, architecture and some royal ceremonies.