Abstract: Software Process Assessment (SPA) was conducted prior to Software Process Improvement (SPI) activities to identify the process areas to be improved. The process assessment methods such as ISO/IEC 15504-2 and SCAMPI were available to all enterprises. But they were difficult for most of small organization because of the complexity and the consequent large investment in terms of time and resources. In order to conduct the SPA activities with few efforts in the small organization effectively, this study presented a quantitative assessment model. It was an efficient approach to evaluate the quality of the process execution in the projects for improvement of the organization’s maturity. The project activities and deliverables were identified as organizational standard assessment items which could be tailored for each specific project. The weight was assigned to the tailored assessment items and the corresponding review activities according to importance and priority. Through an effective quantitative approach on the milestone-driven assessment, the compliance score could be obtained based on the characterization of the assessment results from document inspection and interview session. The initial practices results showed that the presented lightweight assessment model was indeed suitable for small organization to support the process assessment and improvement activities.