rigonella foenum-graecum generally known as fenugreek, has been normally cultivated in Asia and Africa for the edible and medicinal values of its seeds. Fenugreek leaves and seeds have been used widely for therapeutic purposes. Fenugreek seed is recognized to show anti-diabetic and anti-nociceptive properties and other things such as hypocholesterolaemic, and anti-cancer. Diosgenin is a steroidal saponin from therapeutic herbs, fenugreek (T. foenum-graceum L.), has been well-known to have anticancer properties. Telomerase activity is not identified in usual healthy cells, while in carcinogenic cell telomerase expression is reactivated. Therefore telomerase illustrates a promising cancer therapeutic target. We deliberate the inhibitory effect of pure diosgenin and fenugreek extract diosgenin on human telomerase reverse transcriptase gene (hTERT) expression which is critical for telomerase activity. MTT-assay and qRT-PCR analysis were achieved to discover cytotoxicity effects and hTERT gene expression inhibition properties, separately. MTT results exhibited that IC50 for pure diosgenin were 47, 44 and 43 µM and for fenugreek extract diosgenin were 49, 48 and 47 µM for 24, 48 and 72 h after treatment. Culturing cells with pure diosgenin and fenugreek extract diosgenin treatment caused in down regulation of hTERT expression. These results indication that pure and impure diosgenin prevents telomerase activity by down regulation of the hTERT gene expression in A549 lung cancer cell line, with the difference that pure compound is more effective than another.