Cell-specific information on quantity and localization of key mRNA transcripts in single-cell level are critical to the assessment of cancer risk, therapy efficacy, and effective prevention strategies. However, most available technologies for mRNA detection rely on cell extraction that inherently destroys the tissue context and provide only average expression levels from cell populations or whole tissues. In this paper, we proposed a novel super resolution concept, second harmonic generation (SHG) super-resolution microscopy (SHaSM), and apply that to detect single short mRNA transcript, Her2 mRNA, beyond the diffraction limit. Nano-sized SHG crystals, barium titanium oxide BaTiO3 (BTO), were functionalized with two complimentary strands of Her2 mRNA after the chemical surface-modification. Dimer schematic was used to improve the specificity of detection and quantification, where two BTO monomers bind to the Her2 mRNA to form a dimer and being visualized via the SHaSM. SHaSM is able to detect single BTO nanocrystal with ~20 nm spatial resolution, and differentiate BTO dimers (Her2 mRNA) from BTO monomers (non-specific bounded BTO nanocrystal) with high specificity.