Uniform ultrasmall monodisperse SrYbF5 and SrErF5 nanocrystals (NCs) were synthesized via solvothermal method using oleic acid as stabilizing agent. Transmission electron microscopy and X-ray diffraction assays reveal that the as-synthesized NCs are of face-centered cubic structure and the cell parameters are 5.608 (SrYbF5) and 5.632 (SrErF5) . Under the excitation of a 980 nm laser, visible upconversion (UC) emission can be observed by naked eyes in Tm3+ or Er3+ doped SrYbF5 NCs. The integrated intensity of infrared emission is nearly two orders of magnitude stronger than that of the blue emission of SrYbF5:Tm3+ NCs. The energy transfer UC emission mechanisms were also investigated.