Son La is located in northwestern Vietnam. There are 6 minority groups living together in Son La, and Black Tai is a dominate minority group (estimated more than 60% population). The black Tai use dyeing plants for coloring food and clothes, contributing to special occasion of community. Through four surveys during 2013-2014, we have recorded 21 plant species out of 12 families, for dyeing textile and food, including unique techniques for blending plant to require purpose colors. How is local knowledge maintained now? We have carried out surveys in communities of black Tai in two Districts, Thuan Chau and Sop Cop to study on K-A-P (Knowledge, Attitude and Practice). There is a major difference between elders and youths in knowledge, and between knowledge and practice in daily life at local communities in Son La Province. The results of surveys have showed how they want to maintain traditional customs.