Dramatic advances in the development of wood plastic composites (WPC) have germinated a great deal of research in this promising field. Using agricultural wastages as filler has a great deal of importance in providing wood plastic composite. In the present study, the 40 wt% pistachio shell flour is used as a filler of high density polyethylene matrix. An attempt is made to investigate the effect of such factors as nanoclay (cloisite 20A), and photo stabilizers on tensile, impact, color fading and weathering Characteristic. To achieve this aim, nanoclay cloisite 20A at levels of 0, 3, 6 Phc, titanium dioxide (Tio 2 ) as a photostabilizer at levels of 0, 2, 4 Phc, and hindered amine light stabilizer (HALS) at levels of 0, 0.25, 0.5 Phc, were analyzed. According to Taguchi’s L9 orthogonal array, nine compounds were selected. Compounds using a melt blending two-step process in a laboratory twin screw extruder were prepared. The specimens of tensile and impact testsprepared using an injection molding machine. From resultsof tensile and impact tests, the No. 5 specimens were the best (consisting 3 Phc nanoclay, 2 Phc Tio 2 and 0.5 Phc HALS). Samples of No. 5wereplaced in Q-Panel as well as control samples (which was without any nanoclay and photostabilizer). The weathering condition was implemented for 1500 hours. Color measurement and tensile tests were done in interval of 250, 500, 1000 and 1500 hours. The finding revealed that the nanocaly cloisite 20A had acted as a reinforcing agent and increasing nanocaly from 0 to 3 Phc caused 27% increase in tensile strength and 11% increase in tensile modulus. Inappropriate distribution achieved as a result of increasing nanoclay from 3 to 6 Phc made a 4% deduction in tensile strength. Increasing nanoclay from 0 to 6 Phc caused 10% reduction in impact strength of pistachio shell flour-plastic composite. At 6 Phc nanoclay, the reinforcing effect of nanoclay is reduced probably due to agglomeration of nanoclay and increasing the ratio of intercalated structure to exfoliated structure. After 250 hours of weathering test, the tensile strength of control and No. 5 samples increased. By following the exposure time the tensile strength of control sample reduced but in the meantime the N0. 5 samples strength remained almost stable. A change in total color difference (?E) of composite (consisting photostabilizer) is from the initial 11.4 to 13.5 after 1500 h, while ?E of control sample changed from 7 to 38. The color change of No. 5 sample was much less than control sample, and it was acceptable too. The water spray had a high effect on color fading of pistachio shell flour-plastic composite. Adding photostabilizer has a definite affection on preventing pistachio shell flour-plastic composite characteristic decrease. Finally, X-ray diffraction (XRD) data reflected that intercalated and semi-exfoliated structures were developed in the fabricated sample under study. Keywords: Wood Plastic Composite (WPC), pistachio shell flour, physical properties, color measurement, weathering test, nanoclay