Wool is one of the most moisture sensitive natural fibers. This paper investigated changes of wool fiber diameter, fabric dimensions and fabric dimensional properties, as a function of moisture regain, temperature and pH. Experiments were conducted on fabrics with different weave structures as well as on fabrics with and without a permanent set. Results showed that the fabrics tended to contract when they were subjected to increased temperature at saturated regain. The degree of contraction appeared to depend on the weave structure of the fabrics and permanent setting treatments. Dimensions of the wool fabrics were also found to be dependent on the pH. Greater fabric dimensions were observed at pH 7.2 than at pH 2.1. The contraction effect was almost reversible when unset fabric samples were measured in pH 2.1. The reasons for the changes of dimensional property were analyzed in terms of changes in wool fiber swelling, yarn crimp and polymer relaxation phenomena with changes in regain, temperature and pH. Industrial implications from outcomes of this research to practical wool processing are discussed in the paper.