[en] The problems of uranium enrichment are generally discussed in the framework of nuclear fuel cycle. As the introduction, the recent topics on uranium enrichment, which were reported by newspapers in 1975, are chronologically presented, and their meanings are discussed. In the second part, the significance of the enrichment problems is discussed from various viewpoints such as safeguard, international economy, and the size of enriching plants in relation to a large amount of required electric power. The world-wide demand and supply of enriched uranium are presented together with the program of nuclear power development and the operational program of enrichment plants. In the third part, the enrichment problems are investigated within the framework of the fuel cycle of light water reactors. Estimated fuel cycle cost and the results of the sensitivity analysis for each factor are also presented on the basis of F. Schwerer's study. Finally, some technical problems on gas centrifuge are discussed, and the world-wide projects including Japanese national project are briefly reviewed. (Aoki, K.)