Because of their excellent temperature behavior, high piezoelectric coupling, low acoustic loss, and high Q-factor, langasite resonators have been the subject of recent interest for use in a variety of applications. The force-frequency effect refers to the phenomenon of frequency changes resulting from the stress applied to the resonator. A clear understanding of this effect is essential for many design applications such as force sensors and stress-compensated resonators. In this article, we report on experimental measurements of the force- frequency effect of various doubly-rotated langasite resonator samples with plano-plano configurations. Comparisons with the available experimental data for the force-frequency effect of quartz resonators are made. The application of this effect for sensors and stress-compensated resonators is also discussed.