Petri nets provide executive facilities for simulation of causality, non-determinism and parallelism in discreet systems. Since they are a mathematical model in substance, they offer theory, which can be successfully used to verification of models. Executability of Petri nets predestinates them for simulation and fast prototyping. Object Petri nets represent rather complicated class, based on hierarchical and high-level Petri nets. However their complexity is balanced by their ability to identify significant characteristics of system model and to visualize it in a graphic representation.Tools currently applied to modeling, simulation and verification of various Petri net variants use language PNML (Petri Net Markup Language) as an interchange format. However PNML is not capable of expression of object Petri net. This paper introduces prototype of XML-based language for modeling of parallel object-oriented systems described by object Petri net. This language, based on PNML, was named OPNML (Object Petri Net Markup Language).