The research area of this master work is problems of information processing in County State Tax Inspectorate and their resolution approaches. The aim of this work is to find the best approach, to create appropriate software to resolve theses problems and to fulfill user’s needs. The main problems of information processing were determined during County State Tax Inspectorate business analysis: • usable legacy information systems imperfect integration and functionality; • some information not computerized processing. After analyzing many approaches three tiers client-server software architecture, internet technologies and relational databases integration was chosen for new information system implementation. Internet browser is used for user interface on client side. All business logic was placed in middle tier. Server side scripts are used for interaction with system new database and legacy database which is working in Oracle DBMS environment. Microsoft ASP technology is used for server-side scripting. Legacy database reverse engineering was accomplished for this database documentation. County State Tax Inspectorate intranet portal users can do data operative registration and processing, quick report formation. The modern CASE tool Rational Rose 2002 Enterprise Edition was used from business analysis to new information system project creation that will help for system maintenance and future development.