Oral squamous cell carcinoma (OSCC), an aggressive epithelial malignancy, is the most common oral cancer, accounting for at least 90% of total cases. Survival has remained at less than 50% and quality of life has been poor. This outlook is due to delayed diagnosis when the disease has already reached an advance stage. Thus, early detection and non-invasive screening tool can be crucial for each patient. Many studies have shown significant decreased methylation levels of long interspersed nuclear element-1s (LINE-1s) in many types of cancerous tissue, including oral rinse of oral squamous cell carcinoma. This study aimed to explore the methylation levels of LINE-1s in the buffy coat and plasma of OSCC patients. Moreover, the level of buffy coat, plasma, and oral rinse within an individual were also investigated. Here, LINE-1 hypomethylation level in oral rinse of OSCC patients (N= 37) was confirmed. In buffy coat and plasma of the cancer patients, the levels were insignificantly increased when they were compared to those of controls (N=45). Moreover, new information of partial methylation pattern of LINE-1s was also reported, suggesting the different gaining and losing methylation processes between normal and cancer. By including this important knowledge with overall methylation level, it was found that the levels of complete unmethylated (98 bp product) LINE-1s were significantly higher in all three DNA sources of OSCC patients. Not only that, complete unmethylated LINE-1s was an improved biomarker for distinguishing cancer from normal DNA, in the presence of other contaminated DNA types. With simply and non-invasively obtained oral rinse sample, the level of LINE-1 complete unmethylated sequence was a distinctive candidate for detecting early stage OSCC and provided sensitivity as well as specificity reaching 80%-90%. Therefore, a better survival and quality of life of OSCC patients might be achieved.