The article presents a method for constructing a model of an object-oriented program in terms of multilabeled Petri nets. Only encapsulation - one of the three concepts of object-oriented paradigm - is considered. To model a different aspects of encapsulation a Petri net structured object is proposed. It consists of a Petri net defining its behavior and a set of organized access points specifying its structural properties. Formal composition operations to construct a program model from the models of its methods, classes, objects, functions, and modules are introduced and a source code translation algorithm to Petri net representation is proposed. A special section of the article considers in detail a process of model construction of a real object-oriented program (OOP). Source code of the program, figures with Petri net objects modeling different elements of the program and the resulting model of the program are presented.