Lee, L. Morton, D.S. Ng, M.L. Zhang, L. JACoW Publishing Geneva, Switzerland In-vacuum actuators are under consideration for operating the bending flexturs of the new Kirkpatrick-Baez focusing mirrors as part of the upgrade to LCLS-II. To achieve an mechanical accuracy of better than 10⁴, the characteristics of the actuators need to be explored. We designed a testing procedure in terms of both setup and actuator excursion program to understand various behaviors of the actuator in a simulated typical operating condition. Multiple independent sensors were used, including optical linear encoder, laser interferometer and capacitive sensors. In this presentation, I will show the testing procedure and results obtained for a commercially available high-precision leadscrew type in-vacuum linear actuator with a stroke of 10 mm and a resolution of 2.5 nm. It was found that under typical static operation conditions, an accuracy of 10⁴ can be achieved without external encoder feedback. Detailed behaviors regarding repeatability and backlash are also discussed.