Honey has become popular as a potential treatment for several ailments, including cancer. Honeys from different parts of the world have been shown to have different anti-proliferative, immune-modulatory, and anti-inflammatory actions. Yemeni Sidr honey (YSH) is world-renowned for its anti-inflammatory activity and has been suggested to have anti-cancer activity, although empirical evidence is lacking. We tested three YSH samples by HPLC to show they contained similar sugars and an overlapping group of phenolic and flavonoid components, as described previously. YSH’s apoptotic and anti-proliferative activities were measured in in vitro models of cancer growth. The treatment of breast cancer cell lines (MDA-MB-231 and MCF-7), a cervical cancer cell line (HeLa), and mouse melanoma cells (B16-BL6) with 1% (w/v) YSH in media for 48–72 h almost completely inhibited cell proliferation and promoted cell apoptosis. In contrast, a non-malignant HBL-100 cell line was more resistant to treatment with YSH. This suggests that YSH may be a good candidate as an anti-cancer treatment, which requires further study.