Ready mix concrete in hot weather countries, such as United Arab Emirates (UAE), is usually subjected to high temperature during its transportation to construction sites. In some cases, due to traffic and location of construction sites, concrete mixing may be prolonged. As such, concrete under such harsh environments (as high temperature and prolonged mixing) suffers from severe slump loss, which may affect its mechanical properties. In this paper, the effect of polycarboxylate-based superplasticizer on rheology and compressive strength of concrete under hot weather was investigated. Ordinary portland cement and fly ash (FA) were used as cementitious materials. Concrete mixtures were made with a water/binder ratio of 0.36. The concrete mixtures were mixed in a walk-in environmental chamber using a drum mixer. The investigated temperature was 40 °C. The compressive strength of concrete was taken at 3, 7 and 28 days. The results show that both rheological parameters and compressive strength are influenced by variation of superplasticizer dosage. While compressive strength increased when superplasticizer dosage increased, torque resistance and flow resistance decreased.