Early detection and treatment are of great importance in the management of osteoarthritis (OA). The current study aims to evaluate the relationship between serum circRNA hsa_circ_101178 and the severity of OA. Western Ontario McMaster University Osteoarthritis Index (WOMAC) pain scores and Kellgren-Lawrence (KL) grading system were used to evaluate the symptomatic and radiological severity of OA patients. RT-PCR was carried out to explore the level of hsa_circ_101178 in serum and synovial fluid (SF) of OA patients. Spearman's correlation assay was used to analyze the correlation between serum hsa_circ_101178 and WOMAC score or KL grading. The diagnostic value of serum hsa_circ_101178 was evaluated using receiver operating characteristic (ROC) curves. Serum and SF hsa_circ_101178 levels were significantly higher in OA patients than those in controls. Further study showed a positive correlation between serum and SF hsa_circ_101178 levels. Moreover, serum hsa_circ_101178 were positively correlated with the severity of OA according to KL grading. Meanwhile, serum hsa_circ_101178 was also positively correlated with WOMAC-pain scores. ROC analysis showed the AUC of serum hsa_circ_101178 was 0.835 in screening OA patients from controls. Upregulation of serum hsa_circ_101178 may play a crucial role in the pathogenesis of OA and can be a useful biomarker for early diagnosis of OA.