The water adsorption into pore spaces in brittle rocks affects wave velocity and transmitted amplitude of elastic waves. Experimental and theoretical studies have been performed to characterize moisture-induced elastodynamic variations due to macroporous effects; however, little attention has been paid to the manner in which wetting of nanopores affects elastic wave transmission. In this work, we extend our understanding of moisture-induced elastic changes in a microcracked nanopore-dominated medium where 80 % of the surface area exhibits pore diameters (also include microcrack widths) below 10 nm. We study acousto-mechanical response resulting from a gradual wetting on a free-standing intact Herrnholz granite specimen over 98 h using time-lapse ultrasonic and digital imaging techniques. Linkages between ultrasonic attributes and adsorption-induced stress/strain are established during the approach of the wetting front. We find that Gassmann theory, previously validated in channel-like nanoporous media, does not work properly in predicting the P-wave velocity increase of microcracked nanopore-dominated media at ultrasonic frequency. However, squirt flow – a theory recognized to characterize wave velocity increase and attenuation in microcracked macropore-dominated media at the pore scale – also accounts for the observed increase of P-wave velocity in microcracked nanopore-dominated media. The transmitted amplitude changes in direct P waves are explained and predicted by the elastic wave propagation within P-wave first Fresnel zone and reflection/refraction on the wetting front.