  Quantum secure direct communication is the direct communication of secret
messages without first producing a shared secret key. It maybe used in some
urgent circumstances. Here we propose a quantum secure direct communication
protocol using single photons. The protocol uses batches of single photons
prepared randomly in one of four different states. These single photons serve
as a one-time-pad which are used directly to encode the secret messages in one
communication process. We also show that it is unconditionally secure. The
protocol is feasible with present-day technique.
