Starch has been the subject of intensive research over many decades due to the fact that nativernstarches are diverse, biodegradable, applications are enormous and modifications to starch arernnumerous. In this study, Plectranthrus edulis (P.edulis) starch has been chemically modified underrnmicrowave heating with the aim of determining its potential for sustained release application. Itrnwas chemically modified by microwave-assisted acetylation using acetic anhydride as acetylatingrnand sodium hydroxide as a catalyst. The reaction conditions were optimized for maximizing therndegree of substitution (DS) and the DS selected were 1.77 and 0.44. rnThe prepared starch acetate (SA) were evaluated and compared with the native P. edulis starchrnand standard excipients in terms of various physicochemical characteristics including the chemicalrnstructural changes, powder properties, swelling power (SP) and solubility, moisture sorption rnpattern, compactibility and drug release properties. The Fourier transform infrared (FTIR) spectrarnof the modified starches verified the structural change in the starch molecules resulting fromrnacetylation. The x-ray diffraction (XRD) and differential scanning calorimetry (DSC) studiesrnshows acetylation reduced the formation of intermolecular hydrogen bonds and thereby resultedrnin the slight destruction of the ordered crystalline structure. The results of the powder propertiesrn(Carrâ€™s index and Hausner ratio, angle of repose and Kawakita analysis) indicated that acetylationrnimproved the flow property of P. edulis starch. Moreover, microwave-assisted acetylationrnappreciably increased starch SP at a lower DS 0.44 than higher DS 1.77. Modification alsornincreased solubility of native P.edulis starch. The water uptake of the P.edulis SA powders slightlyrnincreased with relative humidity (RH) at lower values but increased significantly at about 100%rnRH. rnThe effect of DS on the compactibility and drug release retardant effect were also evaluated byrnusing anhydrous theophylline as model drug. The plain tablets of SA DS 1.77 shows higher tensilernstrength than the SA DS 0.44 tablets and it also shows significant tablet properties than nativernP.edulis starch tablet which reflected the better compactibility of the former modified starch. Plainrntablets of SA DS 0.44 and microcrystalline cellulose (MCC) (Avicel PH 101) were completelyrndisintegrated within few min while those made of SA with DS 1.77 and ethyl cellulose (EC), didrnnot disintegrate at all during the measurement time of 2 h. The tensile strength (19.81 Kg/cmrn) ofrntablets containing 20% of theophylline and 79.5% P. edulis SA DS 1.77 with crushing strength of rn150.2 N was significantly higher than tablets with crushing strength of 51.1 N because the tabletsrnwith crushing strength of 51.1 N has the highest porosity when compared to tablet with crushingrnstrength of 150.2 N. The tablets of SA DS 1.77 has the highest tensile strength and the lowestrnporosity than tablets of SA DS 0.44 at the same percentage composition of theophylline and P.rnedulis SA which indicate the effect of DS. rnThe in vitro release rate was found to be significantly related to the DS and crushing strength,rnhence more sustained release (SR) of the drug was observed with the matrix incorporated with SArnof higher DS and highest crushing strength. The drug release rate of theophylline changed fromrnrapid release to sustained release as the DS increased from 0.44 to 1.77 and as crushing strengthrnincreased from 51.1 N to 150.2 N. The drug release rate also increased as the SA DS 1.77rnpercentage decreased from 79.5 to 59.5% (w/w). Further the drug release data were fitted to fivernkinetic models. Among the various drug release kinetic models applied, the best linearity wasrnfound with Higuchiâ€™s plot (Rrn2 rn= 0.9988) indicating the release of drug from the matrix as a squarernroot of time dependent process based on Fickian diffusion and based on Korsemayerâ€“Peppasrnmodel the release mechanism observed was anomalous diffusion (diffusion coupled withrnswelling). Therefore, it was concluded that P. edulis SA could have a potential for use as arnsustained release excipient.