We researched contribution of a charge transfer (CT) effect to desorption/ionization mechanism in our ultra-high sensitive laser desorption/ionization mass spectrometry based on surface plasmon (SP) excitation (SPLDI-MS). A quantity of CT electrons between a metal surface and sample molecules estimated from Raman measurement is correlated to a mass signal intensity of sample molecule in our SPLDI-MS method. A sample system with a larger quantity of CT electrons gave a higher mass signal intensity. Efficient use of the CT effect would lead to development of a higher sensitive SPLDI-MS and this development would contribute to advancement of various fields. [DOI: 10.1380/ejssnt.2009.93]