The superconductingRb3C60fullerene crystals with a transition temperature of30.5±0.2&hthinsp;Kwere well prepared. We found that the magnetization curves,−4&pgr;M(H),in a wideH–Tregion can be represented to an universal temperature-independent curve with the scaling factor&sqrt;2Hc(T).This scaling behavior is consistent with the prediction of Ginzburg-Landau theory and Hao-Clem variation model. The thermodynamic critical fieldsHcat various temperatures were precisely determined from the−4&pgr;M(H)curves according to the theoretical fitting of Hao-Clem model. Temperature dependence of thermodynamic critical fieldHc(T)in10&hthinsp;K⩽T⩽30&hthinsp;Kis in good agreement to the two-fluid model and BCS theory. However, the best fit is the power-law relation ofHc(T)=Hc(0)*[1−(T/Tc)]&bgr;,whereHc(0)=2344±19&hthinsp;Oe,Tc=29.62±0.07&hthinsp;K,and&bgr;=0.8682±0.008.©1999 American Institute of Physics.