In recent years, olive cultivation has spread globally because of increasing popularity of the health benefits of olive oil. Accordingly, large amounts of olive by-products, such as leaves, branches, and pomace, are being produced by the olive industry. The discharge of this agro-industrial waste into the environment results in ecological repercussions. However, these by-products are potential sources of phenolic compounds as antioxidants for food and cosmetic applications. Their extraction can result in the production of high value-added natural ingredients and a reduction in their harmful environmental impact. Microwave-assisted extraction method has attracted growing interest for extracting these phenolic compounds from plant materials. The purpose of this study was to extract phenolic compounds from olive by-products by maceration and microwave-assisted extraction methods and to compare the phenolic yield obtained with these two methods. The results showed that microwave-assisted extraction could extract a higher yield of phenolic compounds in a much shorter time compared with maceration extraction (10 min instead of 1 h). In addition, the amount of phenolic compounds obtained by microwave-assisted extraction increased with increasing microwave power. Indeed, the extracts obtained were shown to exhibit high antioxidant activities. These collective results indicate that microwave-assisted extraction has a higher extraction efficiency of phenolic compounds from olive by-products compared with the maceration method.