Species of the genus Phyllanthus (Euphorbiaceae) is known popularly in Brazil as "Quebra Pedra" (Break-stone) and indicated for the treatment of renal lithiasis. P. niruri and P. amarus have been studied in Brazil and around the world regarding pharmacologycal activity, due to folk uses. Drying and storage parameters intend to provide a standard raw material with high quality. The storage condition can determine the durability of raw material and relative humidity is one of the most important factors. The aim of this study was to determine the final percentage of humidity and the desorption isotherms. The species were cultivated on experimental field at CPQBA/UNICAMP. The experimental area was harvest and the aerial part was dried in 50ºC until constant weight. After dried, the final humidity was determined. The equilibrium moisture had been determined by static gravimetric method, with a range of relative humidity from 10 to 90%. The most commonly used equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) equations were compared with their ability of best fiting the published sorption data for selected medicinal and aromatic plants. The best-fitted equation identified for P. amarus was Hasley (9,3%), and for P.niruri was GAB (8,9%).