Performance of RPCs operated at the YangBaJing Laboratory

The ARGO-YBJ experiment will be installed at YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China), 4300 m a.s.l. . It consists of a full coverage of about 10^4 m^2 realized with RPC chambers. A small carpet of about 50 m^2 has been operated at YangBaJing in order to check the RPC performance in these high altitude conditions. Results concerning efficiency and time resolution are reported.