Microwave-assisted hydrothermal synthesis is a method that has been showing increasing interest among scientists, mainly because of its simplicity, reduction in synthesis time, and, most importantly, the ability to control synthesis conditions. Manipulating with synthesis conditions, for example by adding different substances such as natural plant materials, it is possible to control the size, shape, and composition of the final product. Implementation of various plant materials in the synthesis process has attracted much attention due to their environmentally friendly and non-pathogenic nature of product obtaining and thus represents the latest trend in the development of green synthesis techniques. The hydrothermal microwave method was used for the synthesis of iron oxide nanoparticles in highly alkaline media with the addition of plant material from Dalmatian herbs. Product characterization was performed by Fourier Transform Infrared Spectroscopy (FTIR) and Powder X-ray Diffraction (PXRD), followed by Rietveld analysis to determine the composition and crystallography of the particles. To obtain information on the morphological characteristics of the product, such as the size and shape of the particles, Field Emission Scanning Electron Microscope (FE-SEM) was used.