Internal friction in two tholeiitic basalts from Deccan Traps (India) was measured at 1.3 Hz in the temperature range 500¿--900 ¿C. The results gave two attenuation peaks, one at approximately 620 ¿C and the other near 830 ¿C. The peaks are attributed to bimodal grain size distribution. (In contrast, polycrystalline alumina with a single grain size distribution gave one attenuation peak at 810 ¿C.) Grain boundary sliding, in the presence of an intergranular fluid phase, is suggested as the possible mechanism of anelasticity in the basalts. With this assumption, we estimate the viscosity of the palagonite glass in the basalts to be 1.7¿1013 P in the temperature range 600¿--640 ¿C and 2.6--5.0¿109 P in the temperature range 820¿--840 ¿C. These estimates are in general agreement with direct measurement of viscosity in tholeiite basalt by Scarfe (1977). ¿ American Geophysical Union 1987