A novel photothermal microactuator based on microscopic photothermal expansion is developed. A theoretical model of photothermal expansion for photothermal microactuator is established. Using finite element analysis and numerical method, the expressions of the temperature distribution and the linear thermal expansion are deduced. A photothermal microactuator of 1200?μm length is fabricated by using an excimer laser micromachining system. According to the parameters of the laser and the photothermal microactuator, a theoretical relationship between the expansion and the laser power is calculated. The results indicate that the photothermal microactuator deflection （corresponding to expansion） is approximately linear with the laser power irradiating the expansion arm, according with theoretical predictions quite well. As an application, a Biswitch like photothermal microactuator is built and the successful photothermal microactuation experiment shows the Biswitch function can be realized.