J. Khademzadeh Yeganeh* 1, M. Sadeghi2, H. Kourki2 1Department of Polymer Engineering, Amirkabir University, Tehran, Iran 2Department of Civil Engineering, Amirkabir University, Tehran, Iran* Corresponding author: J. Khademzadeh Yeganeh (jkh. yeganeh@ yahoo. com) ABSTRACT: The unabated growth in the use of plastics in recent years is of considerable concern because of the difficulties involved in waste disposal. Increasingly, plastics are replacing wood, glass, paper, and metal in numerous applications, especially in packaging. One of this plastics are high impact polystyrene (HIPS) whish is a common component in consumer electronic housings and automobiles. For reducing its waste and decreasing environmental problems we can use it (HIPS) in modification of cement mortar. Cement mortar was modified using recycled high impact poly styrene (HIPS) in powder form. Mixtures with polymer–cement ratios of 10, 15, and 20 wt.% were investigated for changes in compressive properties and adhesion to steel rebar. Compressive tests indicated an increase in Young’s modulus for samples with 10% and 15% HIPS. Adhesion strength to the steel rebar decreased on adding the HIPS. However, when the HIPS was treated with maleic anhydride, an increase in adhesion strength was obtained. The decrease in adhesion of the untreated HIPS-modified cement to steel was attributed to the disruption of the interface between the cement mortar and steel rebar. Addition of 5% nanoclay increased both compressive Young’s modulus and adhesion strength to the steel rebar.