Type II diabetes mellitus (T2DM) is one of the most common underdiagnosed metabolic diseases due to lack of recognizable symptoms in the early stage. T2DM can be largely prevented or controlled by diet or regular exercise at early stages, but often goes undetected for years, causing high rates of complications and mortality. Hence, a valid noninvasive early detection approach is urgently needed. In this study, we explored noninvasive detection of T2DM by salivary transcriptomic diagnostics. Salivary mRNA biomarkers were discovered by comparing microarray profiles of salivary transcriptomes in 13 T2DM patients and 13 healthy controls. The marker candidates selected from the microarray analysis were then subjected to verification in the original 26 samples using reverse transcription quantitative real-time polymerase chain reaction. Four up-regulated and two down-regulated mRNA biomarkers were validated. The logistic regression model showed that the combination of four identified biomarkers (KRAS, SAT1, EGFR, and PSMB2) could significantly distinguish T2DM patients from the healthy controls, yielding a receiver-operating characteristic-plot area-under-the-curve value of 0.917 with 100% sensitivity and 77% specificity. In conclusion, RNA signatures in saliva could serve as biomarkers for the detection of T2DM with high sensitivity and specificity, and offer a feasible means for early T2DM detection.