This article details our work in studying the plasticization of Poly(vinyl chloride) (PVC)/Polymethyl methacrylate (PMMA) blends with bio-based acetyl tributyl citrate (ATBC) in place of conventional plasticizers such as di(2-ethylhexyl) phthalate. PMMA was blended with PVC in various ratios from 0 to 100 wt% by melt compounding with or without the plasticizer ATBC. Both the glass transition temperatures of the blends (differential scanning calorimetry) and Ta (dynamic mechanical thermal analysis) are consistent with a miscibility of the components, and Fourier transforms infrared spectroscopy studies show that there are specific interactions in the PVC/PMMA blends favoring the miscibility. The thermal degradation of the blends was studied by thermogravimetric analysis that shows the thermal degradation of rigid and plasticized PVC/ PMMA is a process composed of two-steps and that PMMA exercises a stabilizing effect on the thermal degradation of PVC during the first step by decreasing the rate of dehydrochlorination. J. VINYL ADDIT. TECH-NOL., 00:000-000, FIG. 6. Ta of rigid and plasticized PVC/PMMA blends. FIG. 7. FTIR spectra of rigid and plasticized PVC/PMMA blends: 1-neat PVC, 2-90/10, 3-75/25, 4-50/50, 5-25/75, 6-10/90, and 7-neat PMMA.