Electrospray-assisted laser desorption ionization (ELDI) is a technique which combines laser desorption with subsequent electrospray ionization. It is useful for directly detecting small and large molecules in solid or liquid samples under ambient conditions. In this paper, the detection of the protein molecules desorbed on a dry protein spot by using pulse laser energies of up to 300 μJ was demonstrated. The influences of organic and inorganic matrices, the laser energy, the laser wavelength, and the sample plate material on desorption of protein molecules from sample plates were discussed. In addition, the effects of the composition of the electrospray solution on the ionization of the desorbed protein molecules were studied.