MALDI mass spectrometry imaging (MALDI-MSI) is a powerful tool to study endogenous metabolites. The process of matrix deposition is crucial for a high-quality imaging result. Commercial instruments for matrix deposition are expensive. Low-cost methods like airbrushing will generate matrix crystals that are too large for high-spatial-resolution imaging. Sublimation may cause some compounds to go undetected because of the lack of solvent. Herein, we utilized a mini-humidifier, costing less than 5 dollars, to deposit matrix for MALDI-MSI. Compared with Imageprep, a commercialized instrument, our device based on the humidifier provided higher sensitivity and much smaller matrix crystals with diameters of less than 10 μm. High-quality ion images with 10 μm spatial resolution were obtained using our method. The enhancement of sensitivity by the humidifier could provide a sufficient amount of ions to perform tandem mass imaging. We also performed MALDI-MS/MS imaging to separate two lipids in mouse brain.