Folic acid (FA) or pteroyl-L-glutamic acid, chemically known as N-[4-[[(2-amino-1,4-dihydro-4-oxo-6-pteridinyl)methyl]amino]benzoyl]-L-glutamic acid, is a water-soluble B vitamin that helps build healthy cells. In this study, a new, simple, easy, accurate, precise, economic and sensitive UV spectrophotometric method for the determination of folic acid in commercial tablets and during dissolution tests is presented. Using a phosphate buffer solution at pH 9.0 it was possible to determine the concentration of folic acid in commercial tablets at a λ_max of 282.5 nm in a linear range of 1.0–17.5 μg ml⁻¹ with a R² > 0.9999 and recovery between 100.6 and 101.1%. The method was also optimized for the quantification of folic acid in dissolution tests in the same linear concentration range. The pH effect on the UV spectra of folic acid solutions was eliminated with a first derivative. This procedure allowed the direct measurement of samples from the dissolution vessel (pH approximately equal to 6) without any pH correction. This method was based on the first derivative of the absorbance at λ = 377.2 nm, yielding an R² > 0.9997 with recovery percentages similar to those presented before. The statistical comparison between the proposed and the HPLC reference method showed excellent agreement and indicates no statistically significant difference in accuracy and precision at a 0.05 significance level.