Abundant lithium-rich clay rocks are explored in the USA, Chili and some other countries. This kind of clay rocks is mainly altered from volcanic ash. The mung bean rocks are hydrolyzed from the sedimentary volcanic ash and are widely distributed in southwest China. To find out whether the mung bean rocks are rich in lithium, the authors studied the mung bean rocks in Tongliang, Chongqing. The test of X-ray fluorescence spectrometer and ICP-MASS shows that the lithium is relatively rich. The content of lithium is 663×10^-6(Li₂O 0.14%) much higher than the cutoff grade of solid and open mining salt mine (0.06%). The total amount of rare earth can reach 500×10^-6, close to the cutoff grade of ion-absorbing type rare earth ore. The result of X-ray diffraction analysis shows that the major ingredients include quartz, feldspar and clay minerals comprising illite and montmorillonite mixed layer and a little illite. The Li concentration of two samples whose clay minerals are pure illite and montmorillonite mixed layer is higher than that of the other samples. Combined with the characteristics of clay rocks and lithium, the authors infer that the lithium exist in ion state and is absorbed by the clay rocks. If the lithium can be comprehensively used, the value of the mung bean rocks will be enhanced greatly.