Rare earth cuprates which show semiconducting characteristics were prepared and their NO2 sensing characteristics have been investigated. In the rare earth cuprates, p-type semiconducting cuprates of Tm or Yb formulated as Ln(2)Cu(2)O(5) (Ln = Tm, Yb) responded to NO2. while the n-type cuprate of Tb did not. In the p-type semiconducting cuprates, the Yb2Cu2O5 cuprate was more sensitive than Tm2Cu2O5. The resistivity of the Yb2Cu2O5 cuprate decreased monotonically with the increase of NO2 gas concentration. In contrast to NO2 sensing, the Yb2Cu2O5 cuprate did not respond to NO at all. The NO2 sensor comprised of the p-type Yb2Cu2O5 cuprate showed a continuous and accurate NO2 detection with high selectivity.