In recent years, many countries have faced inextricable problems in how to deal with the rapid increase in the number of different diseases, which mostly result from the environment and food taken daily; thus, eating healthy and clean foods is always a concern of almost every consumer. Consumers usually make their decisions on the basis of the information provided on the packaging. However, for agricultural products, ensuring that they get exactly what is mentioned on the packaging is a really thorny problem. In practice, several standards have been set up to help agricultural businesses and farmers improve their operational efficiency and ensure their food hygiene and safety. Standards such as Global Good Agricultural Practices (GlobalGAP), Vietnamese Good Agricultural Practices (VietGAP), and Hazard Analysis and Critical Control Points (HACCP) usually cover all production processes from farming inputs such as feeding materials, seeds, and related farming activities to the finally packaged outputs. If businesses and farmers are certified to meet certain standards and they strictly follow the guidelines during the production, consumers can trust in their own decisions. However, it is normally unknown if the production closely follows what has been certified or whether there has been any bribery, cheating, or other negative issues hidden for profit purposes because related information recorded or stored in farm log-books may also be erroneous for intentional or unintentional reasons. To overcome the problem, in this paper, we propose a novel method applying blockchain and IoT technology to support the origin traceability of agricultural products at farms. By using sensors and computational codes to read parameters that affect farming processes such as temperature, humidity, solute concentration, and pH, all related information and data used in origin traceability will be recorded and saved in the blockchain system in the form of logs in a ledger through smart contracts. Specifically, the system operates automatically on the basis of installed smart contracts, i.e., recorded data are stored on a blockchain through smart contracts and are free from human intervention. The proposed system has been constructed and tested with highly satisfactory results. Even if some nodes in the system are knocked down for some reason, when the knocked-down nodes are reconstructed, their original data are automatically and fully recovered from their friend nodes. Consequently, our proposed system provides not only an objective mechanism for collecting and storing data but also a secure environment to effectively trace the origin of agricultural products.