Abstract. This paper proposes the use of 3-tier class of system as core software architecture for building Software Product Lines (SPL).  A base for building a SPL is commonality among software products based on 3-tier architecture, use of available industry frameworks, development organization’s “glue” code and developed services needed by most of the software products within the proposed SPL. A software development organization specialized to develop 3-tier (logical tiers) client-server applications for different kind of industries such as: banking, tourism, telecommunications, etc., can benefit from adopting SPL principles. SPL assumes management of commonality and variability among applications belonging to 3-tier SPL. This paper focuses on benefits from well structured source code organization architecture for 3-tier class of system which is based on SPL principles. To illustrate the approach, this paper presents a usage of 3-tier for On Line Transaction Processing (OLTP) software product line, based on Java technology which serves as the implementation platform.