This study aims to find out the K values of 1 x 1 and 2 x 2 laying-in knit fabrics of plain stitch in fully relaxed state. The results are; 1. Both in 1 x 1 and 2 x 2 laying-in plain knit fabrics, knitted with the larger periphery of a feed, the thinner in thickness, the more air-permeability and the more elastic to be recovered from elongation was obtained. 2. Repeating of 24 hrs wetting at 40$^{circ}C$ twice and drying in air at 70$^{circ}C$ for 1 hr gives the fully relaxed state to the fabrics. 3. A tendency to decrease of K$_1$values with increasing SCSL was recognized and the K$_1$values obtained in fully relaxed state were 86-91, 167-174 for 1 x 1 and 2 x 2 laying-in knit fabrics each respectively. 4. The stable dimensions of laying-in knit fabrics are predictable with K values.