In this report, analytical method using ultra-small droplets of pico∼nano liter generated by a piezo-type inkjet, while focusing on our recent reports. At first, the generation of droplets by an inkjet and the analytical characteristics of the use of inkjet were described. Then, an enzyme-linked immune sorbent assay (ELISA) by the use of an inkjet as a nano-pipette. The fabrication method of a three-dimensional ordered micro bead structure and its application to ELISA was described in detail. The third topic is the application of the inkjet to electrophoresis-mediated micro analysis by drop-by-drop introduction for an antigen and a fluorescence-labeled antibody, followed by the immune reaction and separation by electrophoresis and detection. The forth topic is the development of the new concept of digital PCR, which enabled the on-line PCR amplification of single-target DNA without any transfer of the droplets. Finally, the use of the inkjet to generate micro polymer particles with a novel dipped injection method and its application to the controlled release of drug was described.