Sisal natural fiber - recycled pet bio composite is a composite material produced from sisal fiberrnand polyethylene Tere Phthalate (PET) injection pressing and by using hot pressing. Thernrecycled pet has been utilized as the matrix and the natural sisal fiber acts as reinforcement in therncourse of the production of the composite material. The composite material has been made forrnthe house ceiling application. rnIn the investigation the physical properties and optimization the process parameters of the biorncomposite synthesized from recycled Polyethylene Tere Phatalate (pet) and Agave Sisalinarn(sisal) plant fiber for house celling applications, the ratio of the fiber and the pet were15/85,rn25/75and 35/65 and Press times for all sample taken 10 minutes. The sisal fiber treated with 10,rn15, 20 % alkali solution with treatment time 24, 48 and 72 hours. The effects of treatment time,rnsisal to pet ratio and concentration of alkali on internal bonding and flexural bending wererninvestigated by using a full factorial design using Design Expert 7.0.0 and determined thernoptimal value. rnCharacterization of the physiochemical properties of the bio composite was analyzed and thernresults obtained from experiments that internal bonding 1.36N/mmrn2,rn flexural strength 520 N/mmrn2 rnand the fiber has been characterized as 0.75% cuticle, 8% dry matter, 13.1 % moisture content,rndensity of the fiber 1.33g/mrn, tensile strength 600-700 Mpa, yongus modulus 10.40 GPa,rnelongation of 2-3 % and 0.9 % ash content. rn3rnThe obtained products were tested for their physical and mechanical properties such as density, rninternal bonding (IB) according to German DIN 52352 Standard and flexural bending test. Thernresults indicated that all properties of test were coinciding with wood related particleboards. rnThe optimal value of the internal bonding strength and flexural bending strength of therncomposite at sisal to pet composition ratio of 25/75 in %, treatment time at 72hr , alkalirnconcentration 20% and plate temperature of 246 rnrnrespectively.