Infrared absorption spectra of five lithium silicate and six potassium silicate glasses of varying composition (20–35 mole% Li2O and 15–40 mole% K2O, respectively) are examined in the range 1500–100 cm−1. The frequencies of the main absorption bands decrease with an increase of alkali‐metal oxide (M2O) content, with the exception of the −960 cm−1shoulder for the lithium silicate glasses. The pressure dependences to[inverted lazy s]40 kbar, of all the main infrared absorption frequencies, which are pressure sensitive, are found to be positive. The values ofd &ngr;i/d Pare higher for potassium silicate glasses than for sodium and lithium silicate glasses. The effects of pressure are found to be opposite to the compositional effects. The Gru¨neisen mode &ggr;'s, &ggr;i, evaluated from the pressure dependence of the infrared absorption frequencies, are apparently related to the polarizing power of the alkali‐metal ion. The results discussed in light of previous high‐pressure infrared absorption studies of fused silica and sodium silicate glasses clearly indicate that &ggr;i, &ggr;th, and &ggr;HTgenerally increase withM2O content in alkali silicate glasses.