Histological and immunohistochemical studies require high-quality paraffin blocks, where proper fixation of tissue samples with formalin is a key point. However, in some cases, the possibility to preserve biological samples prior to the formalin fixation or to use deposited tissues from biobanks is important. RNA-stabilizing reagent RNALater represents a potential option, but its suitability for pathological and immunohistochemical studies remains underinvestigated. Here, comparative study of formalin-fixed tissues and those had undergone preservation with RNALater was performed for different SCID mice tissues (brain, liver, kidney, and lung) using histological staining (hematoxylin–eosin and Weigert-van Gieson) or immunostaining for b-actin, glial fibrillary acidic protein, and glycosaminoglycan chondroitin sulfate. It was shown that RNALater preservation for 7–14 days was suitable for histological characterisation of mouse lung tissue, whereas all other tissues demonstrated some changes. Immunoreactivity of all the studied tissues was affected to a different extent, and the observed changes were detected at the 7th day already and continued to get worse by the 14th day. Overall, RNALater preservation affects immunogenicity of normal mouse tissues (brain, liver, kidney, and lung) making them unsuitable for immunohistochemistry. Some tissues retain their morphology (lung tissue) or demonstrate moderate changes (brain, liver, kidney), suggesting a restricted suitability of the RNALater-preserved tissues for histological analysis.