Abstract: Paper spray mass spectrometry has received considerable attentions in recent years due to its simple operation, low cost and without tedious sample pretreatment prior to analysis. However, paper spray ionization (PSI) as a type of electrospray-based ionization source, there are few reports on exploring the ionization performance differences between it and two frequently used electrospray ionization (ESI) and nanoelectrospray ionization (nanoESI). Herein the ionization performance of above three ionization sources was compared systematically by using gasolines, myoglobin, cytochrome c and glycidyl azide polymer (GAP) as samples. According to the obtained results, the ionization performance demonstrated the following trend: PSI