The knee joint problem is one of the major problems for elderly people. The labdane 8 (17),12-diene-15,16-dial (hereinafter referred to as “the Labdane”), which is contained in the Japanese white turmeric leaf and rhizome has demonstrated to inhibit degradation of hyaluronic acid. Since hyaluronic acid is important for lubricating joints, the Labdane is expected to have a role of maintaining joint health. Here, we firstly report the clinical effect of the Labdane on knees. In an uncontrolled single-arm open-label trial, 60 healthy subjects (ages 48 to 88 years) with a discomfort in the knee joint received 0.065 mg of the Labdane-rich LTDT (labdane-type diterpene compounds) per day for 8 weeks. The discomfort of the knee joint was measured every 4 weeks from the start of intake until 8 weeks after beginning the test food ingestion using the visual analog scale (VAS). The results of each VAS score were 4.7 ± 2.2 at 0 weeks, 3.4 ± 2.3 at 4 weeks and 2.6 ± 2.3 at 8 weeks. Statistically significant differences were observed at 4 weeks (p < 0.001) and 8 weeks (p < 0.001) against the 0 weeks of intake. No adverse effects were observed. This preliminary study provided a basic finding that taking the Labdane-rich LTDT 0.065 mg/day for 4 and/or 8 weeks in healthy adult men and women with a discomfort in the knee joint is confirmed to be significantly effective and safe.