Simultaneous detection and imaging of multiple intracellular biomarkers hold great promise for early cancer detection. Here, we introduce a four-color nanoprobe that can simultaneously detect and image four types of mRNAs in living cells. The nanoprobe composed of gold nanoparticles functionalized with a dense shell of molecular beacons, which can identify multiple intracellular mRNA transcripts. It shows rapid response, high specificity, nuclease stability, and good biocompatibility. Intracellular experiments indicate that the nanoprobe could effectively distinguish cancer cells from their normal cells, even some mRNAs are overexpressed in normal cells. Moreover, it can identify the changes of the expression levels of mRNA in living cells. The current strategy could provide more-accurate information for early cancer detection and availably avoid false positive results.