Introduction: Alkaline phosphates (ALP) is an intrinsic plasma membrane enzyme found in many tissues such as intestine, placenta, liver, bone and kidney. The molecular weight of these isoenzymes and isoforms is about 230 KD. Generally they are referred to Low - molecular weight isoenzymes.Materials and Methods: Since bilary cholestasis is always associated with plasma level increase in patients, in this descriptive study, from serums of the patients referred to Brujerd pathology Lab in 2001 (104 cases that 80% of them were over 80 years old) and had a high level of bilirubin too, alkaline phosphatase isonzymes of High-Mr and Low -Mr isolated using, gel filtration chromatography by sephacryl S-300 , on a column 50 x90 cm.The activity of ALP was measured by the modified method of Bessy and Lowry. As a result, gel filtration of the patients, serum ALP (High-Mr and Low -Mr) infractions No, 15 and 19 were involved respectively.Findings: Results showed that chromatography patterns of bil .chol. gel filtration has two peaks (fractions No, 15 and 19) but patients who have no bil . chol , have just one peak (fraction No,15). ALP activity in patients with bil. chol. was 12-30 IU/L, while in the others it was 0-2.5 IU/L. Results obtained by the study of serum gel filtration of 104 patients with high bilirubin plasma level indicated that in 24 patients the gel filtration of bil. chol. is in accordance with gel filtration patterns of the patients with bilary cholestasis .Conclusion: Regarding the obtained results, the amount of activity of bilary isoenzymes in bilary disorders is 6-12 times more than in normal individuals, as well as plasma level of isocnzymealkaline phosphatase (Low-Mr) was twice as much as in healthy persons.