The purpose of this paper is to clarify the frost resistance of fiber reinforced cement sidings through an outdoor exposure test, and the relation between the results of the outdoor exposure test and the results of the accelerated freezing and thawing test on frost resistance. The outdoor exposure test was carried out at Sapporo, Kamiiso and Kitami for 10 years, and the accelerated test was performed according to JIS A 5422-1995. 21 kinds of sidings which differ in production methods and raw materials were prepared. The results obtained may be summarized as follows: 1) Sidings having a apparent density above 1.2g/cm^3 are durable to freezing and thawing action in outdoor exposure test and accelerated test. Also sidings containing air-void, preformed cellular plastic spherical materials and wood flake are durable. 2)The results of the outdoor exposure test are not consistent with the results of the accelerated test. It is surmised that there are affectable factors on frost resistance which are not taken account in the accelerated test.
