Masonry-infilled timber frames are widely used for residential houses in underdeveloped rural and mountainous areas in southwestern China. As suggested by the identified dynamic properties of three typical timber houses of this type, the structure can be taken as a dual system in which the masonry infills provide the most lateral resistance, while the timber frame withstands the vertical loads. The seismic damage to the houses, either of masonry or of masonry-infilled timber structures, in a small town near the epicenter of the 2013 M7.0 Lushan earthquake in southwestern China was inspected and compared, in order to show that the masonry-infilled timber houses exhibited much better seismic performance than the unreinforced masonry ones during the earthquake.