Circulating microRNAs in the blood may provide diagnostic and prognostic information about canine neoplastic diseases, and their profiles may be conserved between human and canine species. We performed RT-qPCR to obtain the profiles of circulating plasma microRNA-214 and -126 in total 181 cases of canine neoplastic diseases and healthy controls. MicroRNA-214 levels were high in 2 epithelial tumours (thyroid and mammary carcinomas) and 4 non-epithelial tumours (osteosarcoma, histiocytic sarcoma, chondrosarcoma, and hemangiosarcoma). In contrast, microRNA-126 levels were high in 6 epithelial tumours (mammary, hepatocellular, squamous cell, thyroid, transitional cell carcinomas, and adenocarcinoma) and 4 non-epithelial tumours (osteosarcoma, mast cell tumour, melanoma, and hemangiosarcoma). The diagnostic potential of microRNA-214 was relatively high in sarcomas, whereas that of microR-126 was high in most types of the tumours. MicroRNA-214 and -126 were prognostic predictors in 2 groups (adenocarcinoma and non-epithelial tumours except for osteosarcoma) and 3 groups (epithelial tumours, adenocarcinoma, and melanoma), respectively. Additionally, the microRNA levels did not show a strong correlation with the other clinical parameters. In conclusion, circulating microRNA-214 and -126 have the potential to be diagnostic and prognostic biomarkers for canine neoplastic diseases. Furthermore, their profiles may be key references as well for exploring novel biomarkers for human cancers.