Abstract: The sampling techniques that determine the credibleness of results in testing the net photosynthetic rate (Pn) of plants were seldom discussed.For this reason,the experiment aimed at investigating the daily changes of Pn,and the difference of Pn values among individual plants,leaves of different position on a plant and the test sites on leaf in ramie cultivars.Pn rose to the peak value by 11:00 and declined afterwards,although an increase of Pn was observed in the afternoon but showing varietal difference.Significant difference was observed among individual plants within a cultivar,and among leaves of different position showing the highest Pn values in the fifth to seventh leaves counting from the essentially expanded leaf of plant top.However,Pn showed no evident difference among the five test sites on leaf.Accordingly,it is reasonable to test Pn values of ramie cultivars within the time 9:00—11:00;at least five plants and their fifth—seventh leaves should be measured,and the test site on leaf be focused near the sharp leaf end.Special attention should be paid to the representativeness of sample plants,and the agreements of leaf position for cultivars,treatments and plants;sample leaves be normal in color and shape,free from disease or insect damage.