In the traditional transaction model, a trans action is a flat sequence of the database operations and the executions of trans actions have the ACID(Atomicity, Consistency, Isolation, Durability) properties. But under the real-time environment, these appear unsuitable. A nested transac tion model to support real-time applications is proposed and the properties and the correctness stanadards of nested transactions are presented in this pap er. The priority assignment strategies and the concurrency control protocol for nested real-time transactions are discussed with emphasis.