Post-anthesis high temperature stress is a major limiting factor for grain filling and final grain yield of wheat (Triticum aestivum L.).  However, limited genetic diversity has been identified to increase this tolerance in wheat, thus the wild relatives have been investigated.  Previously, high temperature tolerance was measured in 52 accessions of five Aegilops species.  Ae. geniculata was identified as having tolerance compared to the other species.   This study screened a larger set of 254 accessions of Ae. geniculata for post-anthesis high temperature tolerance.  Two replications of the accessions were screened in growth chambers under full-season optimal (25/19 °C day/night) conditions with a photoperiod of 18 hours.  Two replications of the accessions were grown in optimal conditions, then exposed to high temperature (36/30 °C day/night, 18 hour photoperiod) 10 days post-anthesis for the following 16 days and returned to the optimal chamber.  Measurements were taken of chlorophyll content using a SPAD meter and response to stress of photosystem II was measured by Fv/Fm values obtained with a handheld fluorometer.  Yield components measured were individual kernel weight, number of kernels per spike, and plant yield.  Comparisons were made between optimal and high temperature conditions. Our goal was to identify high temperature tolerant accessions which can be targeted for breeding into wheat.