Plastic recycling system is the worldwide issue, as this is a non-biodegradable material. Hence, there is a need to constantly find innovative ways to recycle and reuse plastic waste. In this study, Polyethylene terephthalate (PET) plastic was reused as a partial replacement of sand in mortar and concrete mixtures. The percentage replacements are 5, 10, 15 and 20 percent (%) were investigated. The mechanical properties of the mortar and concrete samples were assessed. The fresh and hardened properties assessed for mortar are flow, water absorption, flexural strength and compressive strength, On the other hand, the concrete properties assessed are workability and compressive strength on the control sample and 15% PET replacement. Samples were observed for 7, 28, and 71 curing days for mortar and 7, 28 and 56 curing days for concrete. The results showed that the higher the PET content, the lower the flow rate of mortar. The water absorption results indicated that PET contents investigated resulted in good mixes as they were all less than 10% absorption for all testing ages. The flexural and compressive strength results of the 5%, 10% and 15% PET mortar are generally lower than the control sample. However, they still met the target strengths. While 20% PET replacement results are below the target strength. Hence, 5%, 10% and 15% PET can be adopted for mortar production. The 15% PET concrete met the required expectation for workability and compressive strength with 98% compressive strength of control sample obtained after 56 days curing.