Natural rubber (NR) was blended in various ratios with 17 kinds of tackifiers, which were prepared from rosin and terpenes. The blends were heated to various temperatures (20-120 degrees C) in order to investigate their miscibility. The blends were visually observed for transparency or opacity at each temperature and further observed under an optical microscope for any existence of phase-separated structure. Miscibility of the blends is illustrated as phase diagrams in this article. Phase diagrams of all blends investigated in this study were classified into four types : completely miscible, lower critical solution temperature, upper critical solution temperature, and completely immiscible. The miscible range of a. blend system tends to become smaller as the molecular weight of a tackifier increases. The data also indicate that the esters of hydrogenated rosin and of disproportionated rosin show comparatively good miscibility with NR whereas polymerized rosin and its esters have poor compatibility with NR in most cases.