Serum and urine protein abnormalities in dogs with natural Ehrlichia canis infection were studied. Eighteen dogs presented to Chulalongkorn University Veterinary Teaching Hospital (CUVTH) between March 2000 and January 2001 were included. Group 1 was the control group consisted of 10 dogs coming for vaccination at CUVTH. Group 2 consisted of 5 dogs with natural Ehrlichia canis infection. Group 3 consisted of 3 dogs with natural Ehrlichia canis infection with azotemia (without dehydration, heartworm infestation, or cardiovascular diseases). The types and quantities of serum and urine protein were determined using electrophoresis in all three groups before and after doxycycline 10 mg/kg q24h for 14 days. The results demonstrated that dogs in group 2 and 3 had statistically higher level serum globulin, lower serum albumin, increased urine protein-creatinine ratio, higher total urine protein, and loss albumin in their urine when compared with the control group through changes in the size of podocyte in the kidney glomerulus without immune complex deposition.