The mixed modifier effect (MME) in the lithium-calcium borosilicate glasses, which have a composition of 0.4[(1-x)Li2O-xCaO]-0.6[(1-y)B2O3-ySiO(2)] with x in the range of 0 similar to 1 and y in the range of 0.33 similar to 0.83, is investigated. The MME manifests itself as a positive deviation from linearity in the activation energy of electrical conductivity (Ea(sigma)) and as a negative deviation from linearity in the fraction of four-coordinated boron (N-4), glass transition temperature (T-g), dilatometric softening temperature (T-d), Vickers microhardness (H-v), dielectric constant (epsilon), and dielectric loss (tan). Moreover, the deviation, which exhibits a maximum at [CaO]/([CaO]+[Li2O])=0.5, is enhanced with increasing [SiO2]/[B2O3] ratio in the glass network. The observed MME in T-g, T-d, and H-v are attributed to the bond weakening in the network; however, the MME in epsilon, tan, and Ea(sigma) are caused by the obstruction of modifier transport in the glass network.