This study is to examine the warm/cool feeling and thermal transport properties of ten different knitted fabrics for underwear, measuring the thermal conductivity(λ), thermal insulation value(TIV) using Thermo Labo II type machine. The moisture transmittance and the air permeability were also measured to evaluate the moisture/air transport properties in the knitted samples. Furthermore, the qmax and TIV of specimen were measured after cyclic laundering in order to evaluate the end-use performance of knitted fabrics for under wear. The experimental results were analyzed statistically to relate the thermal properties and moisture/air transport properties, relative humidity, thickness of air layer, etc. The summarized results of this study are as follows: 1. The TIV of knitted fabrics for underwear showed that the smaller the bulk density and the thicker air layer the better the thermal insulation. Regardless of materials, about 150% increase is observed in TIV about 8mm of air layer. And constant decrease in observed in TIV of knitted fabrics for underwear as the relative humidity(RH, %) increased, but dull decrease is observed in TW for more than 65% RH. Particularly, cotton/synthetic blended fabrics showed remarkable decrease as compared with pure cotton and wool fibers 2. The TIV of knitted fabrics for underwear has negative correlation with transport properties such as thermal transmittance($textsc{k}$), moisture transmittance(Mt) and air permeability(Ap). The relation between the TIV and these properties is shown as the following regression equation. TIV( % ) =O.0307($textsc{k}$) -O.3594(Mt) +0.5778(Ap) 3. Remarkable increases are observed in TIV of knitted fabrics for under about l~5 cycles of the repeated laundering, but slack decrease are observed in TIV more than 5 cycles of repeated laundering. While remarkable decrease are observed in the qmax about l~5 cycles of the repeated laundering, but slack increase are observed in the qmax more than 5 cycles of repeated laundering. Particularly, lxi rib stitch and interlock stitch knitted from pure cotton and wool respertively showed remarkable change as compared with double layer or triple layer knit structure made of cotton/synthetic blended fibers.