Beryllium-7 in Be(OH)₂ gel was compressed in diamond-anvil pressure cells up to 442 kbar at room temperature. By counting the activity of ⁷Be, the decay rate for the conversion of ⁷Be to ⁷Li via electron capture was measured. The decay constant of ⁷Be, λ, was found to increase, but the rate of increase decreased with increasing pressure. A quadratic regression of the data yields (λ−λ₀)/λ₀=(4.87×10⁻⁵)P−(5.9×10⁻⁸)P², where the subscript zero denotes zero pressure and P stands for pressure in kilobar. Thus, λ of ⁷Be increases by about 1% at 400 kbar. The observed data set can be rationalized by an increase in electron density near the nucleus of ⁷Be at high pressures. This result may bear some implications for the conversion of ⁴⁰K to ⁴⁰Ar, which has been widely adopted to date geological events.