Introduction: Cat’s claw (Uncaria tomentosa) is a native amazonic plant that exhibits anti-inflammatory and antitumor properties. Patients and methods: This prospective phase II study assessed the effects of a 100-mg dose of a dry extract of U. tomentosa three times per day on individuals with advanced solid tumors, with no further therapeutic options and with at least 2 moths life expectancy. We used the EORTC QLQ C30 and FACIT-F questionnaires to assess the participants’ quality of life, the HADS questionnaire to assess their anxiety and depression and the Pittsburgh index (PSQI) to assess their sleep quality. In addition, several biochemical and inflammatory parameters were analyzed. Results: We recruited 51 volunteers; their median age was 64 (33-85) years old, and 47% were females. Their scores on the Karnofsky scale were equal to or less than 80% for more than 65% of the volunteers. Treatment caused an improvement in the patients’ overall quality of life (p= 0.0411) and social functioning (p= 0.0341), as assessed by EORTC QLQ C-30, and a reduction of fatigue (p= 0.0496) by the Chalder Fatigue Questionnaire. None of the biochemical or inflammatory parameters assessed (interleukins 1 and 6, C-reactive protein, tumor necrosis factor alpha, erythrocyte sedimentation rate and alpha-1-acid glycoprotein) exhibited significant changes. No tumor response was detected according to the RECIST criteria; however, the disease stabilized for more than eight months in four participants. The medication was well tolerated by most patientes. Conclusion: We conclude that use of cat’s claw might be beneficial for patients with advanced cancer because it could improve their quality of life and reduce fatigue. The mechanism of this action does not seem to be related to the anti-inflammatory properties of this plant.