A series of Bi0.2Ca0.8MnO3 samples with average grain size ranging from 38 to 1500 nm have been prepared by the sol-gel method and their structure，electrical transport，and magnetic properties were investigated. It is found that with the reduction of the grain size，the charge ordered phase gradually diminishes till it is completely suppressed，leading to appearance of the spin-glass state at low temperature. These behaviors are discussed in terms of the martensitic transformation and surface effect.