In this paper, we focus on our R&D activities in the field of high-temperature superconducting (HTS) power transmission cable, and summarize its present status. Five- to seven-meter cable models and 50-m-long conductors were developed using silver-sheathed Bi-2223 tape wires. A 30-m single-phase cable prototype having a closed cooling cycle was also constructed. Numerical and experimental approaches were carried out to reduce AC losses in these conductors. Based on these activities, we have started a new project to develop a 100-m, 66 kV/114 MVA three-phase power transmission cable system prototype and conduct long-term loading tests. In this project, we aim at certifying its manufacturing ability and its practicability, and also extracting the necessary information for development of a field-level HTS power cable system.