Plant diversity was determined in preserved and utilized forests of Ban Hang Thang Luang (HTL) and Ban Pha Suk (PS), Tambon Phu Fa, Bo Kluea District, Nan province, by using 50 x 40 – m2 sample plot for the respective villages. Utilization information of forest products by the local people was gathered by interviews. At PS, there were 291 plant species in 92 families, in which 149 species were trees. The plant diversity indices of the preserved and utilized forests at upper montane plot (700 msl.) were 3.186 and 3.359 respectively. They were respectively 3.236 and 3.978 at the lower montane plots (500 msl.). At HTL, where 217 plant species of 67 families were recorded, 149 species were present as trees. The plant diversity indices of the preserved and utilized forests at the upper montane plots were 3.186 and 3.359 respectively. They were respectively 3.236 and 3.978 at the lower montane plots. According to the interviews with the villagers within the study areas, the majority of forest products were used as fuel, construction materials and food. Although trunk damage can lead to huge impacts on the forest, trunk was a part of trees that was most likely to be exploited. The community should set guidelines to control the forest utilization not to exceed forest capacity and support tree plantations to decrease disturbance of natural forests for the sustainable use.