A Thomson scattering diagnostic system has been developed for measuring electron temperatures in low-aspect-ratio reversed-field pinch (RFP) plasmas in REversed-field pinch of Low Aspect ratio eXperiment (RELAX). In the range of plasma currents Ip = 50 - 80 kA, the central electron temperature was around 100 eV and, showed a weakly increasing trend as Ip increases. To estimate the central electron pressure pe0, a density calibration was performed from simultaneous measurements with a 104-GHz microwave interferometer. The maximum pe0 increased with Ip up to ∼ 70 kA to preserve the approximate relation pe0/Bθa2 ∼ constant, where Bθa is the edge poloidal field. In the higher current region, pe0 tended to saturate, which may be improved by optimizing minute control of equilibrium in the higher current region.