[en] Sengon wood (Albizia chinensis) is one type of wood that is abundant in Indonesia. Cellulose content in sengon wood is quite high, up to 41.17 %. The process of cellulose extraction from sengon wood can be done through the process of delignification or removal of lignin content. Generally the delignification process is carried out with an alkaline solution at high concentration, high temperature and long time. In order to use lower alkaline concentration and shorter time process, the delignification process can be performed by assisted ultrasound. The purpose of this research is to study the effect of operating conditions (such as temperature and time) of ultrasonic delignification process on cellulose content in the cellulose product. The delignification process was carried out by mixing the sengon wood (40 mesh) with NaOH solution (0.3 M) at a ratio of 1:30 (w/v). The operating conditions used are 30 °C and 40 °C at various times (10-70 minutes). After the delignification process, the product is bleached with NaOCl until the color of product becomes white. The product was analyzed by Chesson method, XRD (X-Ray Diffraction), and SEM (Scanning Electron Microscopy). The results of the analysis showed that the highest crystallinity was 77.05 % at 40 °C for 30 minutes and lignin content was decreased until 0.41 %. (author)