The emphasis of the work is on blockchain technology and the development of an Internet banking application developed in React technologies for frontend, Spring and Java for backend, and Blockchain used to build a private network on which the entire application is based. The first part of the paper deals with an overview of blockchain technology, its advantages and disadvantages. A detailed description of the operation of the blockchain is presented, from the very concept of the blocks of which it consists all the way to the mining process. The concept of cryptocurrency introduced by blockchain and its application both in today's world and in the future where it is assumed to have a great impact on the world monetary system is also explained. Also described is a new concept in the blockchain world called the smart contract and the Ethereum network that first introduces it. The second part of the paper provides an overview of the technologies used to create the application. The first technology described is React, which in this situation was used to create a graphical user interface. Its basic concepts such as components, state and lifecycle methods, which are contained in almost every React component, and methods of conditional rendering using a ternary operator and hooks are explained. The basics of information about the Java programming language developed for the purpose of the WORA concept (write once run anywhere) are also given. It is the nature of applications written in Java that makes this possible because each is translated into bytecode (an intermediate language that can be executed on any Java virtual machine) when compiled. A description of the Spring framework technology used with Java to create a project that was used as a communication portal between the user interface and the blockchain network is also presented. The last part of the paper refers to the application development process and its testing. The structures of projects (frontend, backend, private blockchain network) that have been created, a smart contract written in the Solidity programming language and descriptions of some parts of the code are shown. The entire testing process is described and images are attached to show different aspects of the user interface.