This investigation aimed at examining historical background, past and current traditions, and customs as well as analyzing cultural practices, beliefs, and traditions of the Lao Song ethnic group in Phitsanulok and Phichit Provinces. It was found that the origin of the ethnic group was in the Dam River Plains, Tonkin region, Vietnam, which was a part of the Thai kingdom. During the early Ratanakosin Period (Kings Rama 1-3), the French invaded the region, forcing the ethnic group to migrate to central Thailand several times. Their original settlements were in Phetchaburi and Ratchaburi Provinces. Later on, they moved to settle in other neighboring provinces, including Phitsanulok and Phichit Provinces. The ethnic traditions were based on the beliefs in nature and spirits. “Thaen” is regarded as the highest deity who was believed to be able to create all things and their ancestor spirits were believed to be able to protect members in the family. Paying homage to the deity and ancestor spirits is still conducted nowadays. Rituals to appease other spirits in nature are less practiced and some are no longer conducted. For the living conditions of the ethnic group in the two provinces, their villages were in rural areas. Previously, they resided along the Yom River, where water and public infrastructure were scarce. They were farmers and poor with health problems. For their ethnic cultural practices, they still believe in spirits and souls, paying homage to the “Thaen” deity and to their ancestor spirits in every household. Other beliefs were hardly practiced. Traditions carried out on a regular basis were “Sen Ruan” and “Sen Pad Dong”. Those carried out sometimes were “Kin Dong” or traditional Song wedding and “Pa Hae” or the construction of traditional Song coffins. The villages with strong ethnic traditions were Nong Kha Nang in Bang Rakam District, Nong Hua Pluak in Phothapchang District, and Sa Boraphet in Sam Ngam District.