The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet fully understood. In this study, a series of tests was conducted to evaluate the pullout response of grouted soil nails in a field slope. A new innovative grouting packer system was developed to control the grouted length and maintain the cement grout pressure of the grouted part. By using the grouting packer system, a total of 10 soil nails placed at different soil depths were grouted with different pressures in the field. The pullout results of present field tests and a number of past laboratory tests indicate that the apparent coefficient of friction (ACF) decreases with the increase of overburden stress even though grouting pressure is applied. In addition, when the overburden stress is unchanged, the obtained ACF values in the field tests appear to increase almost linearly with the increase of grouting pressure. After the soil nails were completely pulled out of the ground, the surfaces of the soil nails and surrounding soil were examined. It is found that the water content of the soil samples at the soil–nail interfaces decrease substantially compared to the water content of soil samples in drill holes. Measurement results also show that the failure surfaces of soil nails shifted about 16 mm on average into the surrounding soil due to the application of grouting pressure.