This paper deals with parallel checking of passive constraints in object-oriented databases. It presents a parallel algorithm for constraint checking based on a master-slave technique and discusses its implementation on a parallel object-oriented database system. The system is named PRACTIC and is based on class concurrency. Passive constraints, unlike active database rules, are independent and can be executed using AND-parallelism. Simulation shows that the proposed algorithm offers considerable speed-up, which mainly depends on the number of constraints and the total constraint execution time, while it is only slightly affected from the distribution of constraints and the constraint scheduling policy. Finally, it is explained how the PRACTIC system enhances the algorithm’s performance using features, like nested query parallelism and constraint overlapping.