Abstarct: The aim of this investigation is designing a new optical sensor for determination of palladium (II) ions. A chromogenic reagent 1-(2-thiazolylazo)-2-naphthol (TAN) has been utilized to prepare a novel sensing membrane (optode) by immobilization on triacethylcellulose membrane. The sensing mechanism inveloves the complex formation between Pd(II) and immobilization TAN , which result in the absorbance increasing at 660 nm. Pd(II) can be determined in the linear range between 2.6×10^-4 and 4.6×10^-6 with a detection limit of 3.26×10-6 molL-1 with a response time of 10 min. The sensor can be regenerated by placing the film into a ethylendiamine solution for 4 sec, then placing into a 1.0×10^-3 molL-1 of TAN solution for 5 sec for 15 times. The relative standard deviations for five replicate determinations of 7.5×10-6, 8.5×10-5 and 2.2×10^-4 molL-1 pd(II) were 7.3٪, 8.4٪ and 5.2٪, respectively. The sensor shows sufficient repeatability, reproducibility and operational lifetime of 6 weeks. The sensor was applied for determination Pd (II) in tap water and alloy samples with satisfactory results.