The objectives of this study focused on optimizing extraction conditions (i.e. type of solvent (methanol, ethanol, and water) and their concentration, temperature, time, and the effect of ultrasound-assisted extraction (UAE)) for extracting phenolic compounds of rambutan fruit peel. Furthermore, a procedure to prepare crude phenolic powder from rambutan peel was suggested. Total phenolic content and antioxidant properties of rambutan peel extracts were examined using spectrophotometric methods. Solid phase extraction and high-performance liquid chromatography were used for identifying phenolic compositions in rambutan peel extracts. Methanol 80% had significant effects to obtain higher extraction yields of phenolic compounds. UAE significantly affected the yield of phenolics of rambutan peel with an increase in phenolic content of 15% compared to methanolic extraction (without ultrasound application). Phenolic compounds such as geraniin, corilagin, rutin, ellagic acid, and quercetin were predominant in rambutan peel extracts. An extraction procedure was summed up to obtain 55−64 g of lyophilized powder from 1 kg of fresh rambutan peel. The total phenolic content in this crude phenolic powder was 250−300 mg GAE/g. Its antioxidant activity (at 100 μg GAE/mL) was much higher than those of tert-butylhydroquinone, l-ascorbic acid, α-tocopherol, and ethylenediaminetetraacetic acid (at 100 μg/mL).