Fisetin (3,3′, 4′7-tetrahydroxyflavone) is an active flavanol phytoconstituent, available in the market as a nutraceutical but poor aqueous solubility limits its therapeutic use. Even though sensitive and modern technique based fiestin estimation was reported earlier, there is a need of simple, fast and cost-effective method based on UV-Spectrophotometric technique for routine application. Developed and validated a UV-spectrophotometric method and used for estimation of fisetin from cubosomal nano-formulation, marketed formulation, and strawberry fruits. A standard calibration graph was developed for fisetin using methanol in the 2-10 μg/ml concentration range using λmax 362 nm. The linearity equation for fisetin absorbance was y=0.0947x + 0.005 with a correlation coefficient of 0.9998. The method was accurate as fisetin recovery > 95%, precise and robust as % RSD < 2 for absorbance after a change in analyst, instrument, and wavelength. The fisetin loading and cubosomal entrapment percentage was found to be 99.48±0.23 and 79.83±0.65 respectively. Fisetin estimated in ‘Doctor’s Best ® Fisetin’ was 98.82±0.18 mg per capsule (Label claim 100mg/capsule) and in strawberry 2.59±0.21 μg/gm of its dry powder. We report a new, simple, cost-effective, fast, accurate, and sensitive UV-spectroscopic method for routine quality control of fisetin formulations and other samples.