This investigation was conducted on soil samples collected from different fluvial and lacustrine depositional environments, irrigated for a long-time with either Nile water or wastewaters. The main purpose of this study was to shed light upon the immobilization capability, kinetic behaviour and catalytic efficiency of phosphomonoesterase proteins immobilized on natural soil clay fractions and their synthetic organo-clay complexes. The obtained results could be summarized as follows: **   Immobilization and stabilization capability of acid-phosphatase protein on natural uncoated clay fractions and synthetic organo-clay complexes were higher than that of alkaline-phosphate protein, determined as bovine serum albumin (BSA). **   Immobilization capacity of the more hydrophobic cationic detergent-clay complexes for retention of phosphatase-proteins was greater than those of either less hydrophobic more hydrophilic humic acid-clay complexes or activated-coated clay fractions. The natural uncoated-clay fractions showed the highest binding capacity over all the other complexes. **   Immobilized-phosphatase-proteins on natural clay fractions and synthetic organo-clay complexes have been displayed low catalytic activities in comparison with their free-enzyme states. **   Specific enzyme protein activity (SEPA) in mg PNP released.(mg protein)^-1. hour^-1 of free-acid-phosphatase and its affinity to react with its specific substrate (r-nitrophenyl phosphate) was markedly higher than those obtained of free-alkaline-phosphatase. Immobilized-phosphatase-proteins exhibited lower (SEPA) than the corresponding values of free-enzymes. Stabilized acid-phosphatase protein retained higher residual specific activity (RSEA%) than those of alkaline-phosphatase protein. **   Immobilized-phosphatase-proteins on the more hydrophobic cationic HDTMA-clay complexes exhibited greater (SEPA) values; retained highly (RSEA%) in comparison with either HA-clay complexes or coated- and natural clay fractions, which displayed the lowest values in spite of their highly immobilization capacity for retention of phosphatase-proteins. **   The K_m values in (mmoles L^-1) of immobilized-phosphatase-proteins were markedly increased, however, V_max values in [mg PNP released. (mg protein)^-1-hour^-1] were sharply decreased in comparison with their free-enzyme values. Little profound differences between K_m and V_max values of free- and immobilized-phosphatase-proteins on HDTMA-clay complexes could be discerned. However, on natural clay fractions, they displayed the highest K_m and the lowest V_max values. **   Alkaline-phosphatase protein was highly-sensitive and lowly- resistive for proteolysis, meanwhile, acid-phosphatase has a low-sensitivity and high-resistivity for proteolytic enzyme. Immobilized-phosphatase-proteins on HDTMA-clay complexes displayed more resistance and stabilization against proteolysis related to their free- enzymes, which lost almost their activities. Immobilization on natural clay fractions showed the lowest stabilization and resistance towards proteolysis. No loss in the stabilization and activity of free- and immobilized-phosphatase-proteins were observed against the storage for 125 days. **   Soil specific enzyme activity in [mg PNP released. (kg soil)^-1.hour^-1) of acid-phosphatase was higher than that of alkaline-phosphatase, however, the specific protein concentration of alkaline-phosphatase was greater than of acid phosphatase. This means that acid-phosphatase have much more catalytic efficient in hydrolysis of phosphomonoesters in studied alluvial soils (low protein concentration and high specific activity) than does alkaline-phosphatase (high protein concentration but low specific activity).                 Therefore, immobilized phosphomonoesterase on synthetic organo-clay complexes are strongly recommended to be used for reduction and detoxification of some xenobiotic substances which is considered to be a safe method for clean-up of the environment.