For calculating interface properties from pullout tests, a simple theoretical model is proposed. The model enables calculating of the following material parameters: the parameter of shear stiffness of the fiber–matrix boundary layer, the shear bond strength, the frictional bond strength and the specific interfacial fracture energy. These parameters can be determined from the slope of the load‐slip curve, the maximum pullout load and the corresponding slip value. Slip‐controlled, multiple‐fiber pullout tests were conducted in a closed‐loop test system. The effects of embedment length of fibers on the model‐predicted material parameters were examined. The model predictions were satisfactorily compared with some previously published test data. Copyright © 1991, Wiley Blackwell. All rights reserved