Abstract: The minimum sampling areas (MSA) for the plant communities on barren hillsides of arid valleys in the upper reaches of the Minjiang River were determined using the community species-area curves worked out via 3 curvilinear equations. Results show that to the types of plant communities in the study region,the species-area curve obtained via the equation S=c-ae^-bA is better than the others obtained via other two equations. When the proportional factor(ρ) is set at 0.6, 0.7 and 0.8, MSAs are all smaller than 2 m² and a quadrate can be designed as 1 m × 2 m, that is, the area of the quadrate is 2 m², which is adequate to meet the requirement of the research for precision of 60%～80%. When ρ is set at 0.9, MSAs are obviously smaller than 4 m²,and the quadrate is designed as 2 m × 2 m, that is, the area of the quadrate is 4 m²,which is adequate to meet the requirement of the research for precision of 90%.