We recently reported that 3′-sulfonoquinovosyl-1′-monoacylglycerol (designatedA-5) extracted from sea urchin intestine was effective in suppressing the growth of solid tumors. Although the major fatty acid component of A-5 was a saturated C16 acid, there were five other fatty acids, 14:0, 18:0, 14:1, 16:1, and 18:1, which constitute minor components of A-5. Therefore, it remains unclear as to which of these six fatty acid components of A-5 has the anti-tumor effect. In this study, we synthesized sulfolipids each containing only one of these six fatty acids and tested their cytotoxicity against tumor cells and in vivo anti-tumor effects on nude-mice bearing solid tumors of human lung adenocarcinoma cell line A-549. The IC50 values of all products against tumor cells were more than 10-5M, suggesting weak cytotoxic activity compared with other chemotherapeutic compounds for cancer. On the other hand, in vivo anti-tumor assay showed that sulfoquinovosyl-monoacylglycerols (SQMG) composed of 14:1 and 18:1 (designated SQMG(14:1) and SQMG(18:1), respectively) were significantly effective in suppressing the growth of solid tumors. Our data suggested that these two SQMGs had a substantial anti-tumor effect in vivo, and they are of interest as candidate drugs for anti-cancer treatment.