Among a number of laboratory methods used to estimate the adequacy of heat treatment applied to full-fat soybean (FFSB) protein solubility in potassium hydroxide (PSKOH) is an unofficial method, but it is used by many laboratories due to its simplicity. It has been reported that the results of PSKOH analysis of the same sample of FFSB on the degree of heat treatment vary widely between laboratories. In this study, the original PSKOH method has been modified and subjected to an inter-laboratory test, with participation of 9 laboratories. Eight FFBS samples were processed by dry extrusion at temperatures ranging from 110 to 164°C and analysed on PSKOH. Processed FFSB samples were also assessed in a growth trial with broilers. Analysis of FFSB by the PSKOH method generated for adequately-processed FFSB values between 67.1 and 76.5%. The values above 76.5% corresponded to under-processed and below 67.1% to over-processed FFSB. The PSKOH method generated good precision, i.e. the repeatability and reproducibility limits of 3.48 and 10.86 %, respectively. The modified PSKOH method can be recommended as a reliable indicator for quality control of heat processed FFSB for the use in routine laboratory practice. This study could pave the way for establishing PSKOH as an official method for determining the nutritional value of FFSB following heat treatment.