CD200 is a novel immune-effective molecule, existing in a cell membrane-bound form, as well as in a soluble form in serum, which performs to modulate inflammatory and acquired immune responses. Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the development of large renal cysts and progressive loss of renal function. As defects in cell cycle arrest and apoptosis of renal tubular epithelial cells occur in ADPKD, we asked whether serum soluble CD200 might underlie and effect on ADPKD. Serum soluble CD200 levels were measured in 44 patients with ADPKD and 24 healthy volunteers. Concentrations of soluble CD200 in the serum samples were quantified using an ELISA kit. The mean serum soluble CD200 levels were higher in patients with ADPKD than in the control group (71.4±29.2 and 21.4±5.6 pg/mL, p<0.001). Positive correlation was detected between serum soluble CD200 levels and glomerular filtration rate (r=0.772, p<0.001), and serum albumin level (r=0.466, p=0.001). Negative correlation was detected between serum soluble CD200 levels and serum creatinine levels (r=−0.761, p<0.001), and C reactive protein levels (r=−0.364, p=0.015). In the ADPKD patients group, serum soluble CD200 levels were lower in patients with stage 5 chronic kidney disease (CKD) than in patients with stages 1–2 (p<0.001), 3 (p=0.005) and 4 CKD (p=0.006). Serum soluble CD200 levels were similar in patients with stages 1–2, 3, and 4 CKD (p>0.05). Our results show that patients with ADPKD have activated soluble CD200 levels which were related to renal function and inflammation.