A new extensometer system was developed to measure strains in cruciform specimens under in-plane biaxial loading at elevated temperature. This system incorporates standard axial contact extensometers to provide a cost-effective high-precision instrument. Capabilities include a minimum strain range of 25% and a maximum sensitivity of eight microstrain (μm/m). Allowable environments include elevated temperature, presently tested to 600°C, and pressures from atmospheric to high vacuum. Descriptions of the test facility, modifications, mounting components, and installation procedures are reported. Calibration of the extensometers is described, including setup, error determination, and classification. Test results are presented for a stainless steel specimen. Strain gage and extensometer outputs are compared for static load cases and for combinations of waveform shape, strain range, frequency range, and test duration for cyclic room temperature tests. Elevated temperature results are presented for free thermal growth conditions and for instrument stability during hot cyclic operation. The results are summarized by the following: the new extensometer system calibrated with a maximum error of 0.8%; room temperature correlation with strain gage data yielded an average variation of 58 μm/m; operation under cyclic conditions resulted in tracking errors less than 3%; elevated temperature results compared accurately with theoretical predictions; and, long duration testing proved to be stable.