Telomeres are ribonucleoprotein structures that form a protective buffer at the ends of chromosomes and thus maintain genomic integrity during the cell cycle. Replicative telomere erosion can be compensated by a telomerase. Average telomeres size decreases with age and associated with aging-related diseases such as cancer and cardio-vascular disease. We previously reported that ASTCOQ02 (an Astragalus extract that contains astragaloside IV and cycloastragenol), a telomerase activator showed benefit in an open prospective study on telomere size and cardiovascular impact in healthy volunteers. Here we performed a randomized, double-blind, controlled trial over 6 months comparing the effect of ASTCOQ02 versus placebo on telomere length (TL) in 40 healthy volunteers (mean age 56.1 ± 6.0 years). Twenty subjects received ASTCOQ02 and 20 received placebo capsules. All 40 subjects completed the study with no adverse side effects reported at 6 months. Subjects taking ASTCOQ02 had significantly longer median (P = 0.01) and short TL (P = 0.004) and a lower percentage of short telomeres over the 6 months period whereas placebo group TL remained unchanged. This randomized, double-blind, placebo-controlled trial confirmed that ASTCOQ02 significantly lengthens both median and short telomeres by increasing telomerase activity, and reduces the percentage of short telomere (< 3 Kbp) in a statistically and possibly clinically significant manner. The results of this study also converge with the previous open prospective trial that found zero toxicity associated with intake of ASTCOQ02. ASTCOQ02 warrants further human studies on health, longer life expectancy and healthy aging.