For the last decades, one of the most developed sciences is nanotechnology. . Similar with their respective particles at higher levels, the nanoparticles show biological properties, unique chemical and physical at nanoscale. Calcium phosphates nanoparticles (CaP Nps) are used as a bio nanomaterial in the fields of nanomedicine. One of the human's body most important basic mineral elements in bones and teeth is calcium phosphate. The aim of this study was to determine the relationship between the rheumatoid arthritis (RA) and Alkaline Phosphatase (ALP) level , and study the effect of Cap NPs and Cap NPs particles coated with casein on ALP level in the sera of rheumatoid arthritis patient.. Seventy Rheumatoid arthritis patient (Male and female) with age range (20-55year) and 30 healthy subjects with sex and sex-matched as a control group was included in the present study .The ALP activity, calcium, and phosphate were measured by using a Colorimetric method. The result showed that serum ALP level in the RA group was highly (108.79 ± 30.07 U/L) than the control group (66.74± 19.08 U/L) (p ≤0.01). While in sera of RA patients a non-significant difference in mean values (p˃0.05) of calcium and phosphate level was stated in contrast with that rate in the control group. Anon competitive inhibition effect of both calcium phosphates nanoparticles and calcium phosphates nanoparticles coated with casein were demonstrated. We conclude that CaP NPs has a higher inhibition effect than CaP NPs coated casein on ALP in sera of rheumatoid arthritis patients