Technical Abstract: Drought and high temperature are two major environmental factors that severely limit plant productivity in the US and worldwide, often causing extensive economic loss to agriculture. As global climate change progresses, agricultural production worldwide faces serious threats from frequent extreme weather conditions. Integrated approaches that improve the efficiency of agricultural water use, and development of plant varieties that can alleviate the negative impacts of environmental stresses to maintain yield stability, are essential to sustain and increase agriculture production. Maize (Zea mays L.) is a major crop in the US and worldwide. Its production and yield stability are greatly affected by drought and high temperature stresses. Improving drought and heat tolerance in maize has become one of the top priorities for maize breeding programs in both private and public sectors. Identification of maize germplasm with superior drought and/heat tolerance is essential and prerequisite for such propose. In this report, we evaluated a selection of maize inbred lines for drought and heat stress tolerance under field conditions in 2009 and 2010 and identified several inbred lines that showed high tolerance to drought. Tolerant inbred lines (Tx205, C2A554-4, and B76) were able to maintain relatively high leaf relative water content when subjected to drought stress while sensitive lines (B73 and C273A) showed a rapid reduction in leaf relative water content at very early stage of drought. The tolerant lines also showed significantly greater ability to maintain vegetative growth and alleviate damage to reproductive tissues under drought conditions compared to the sensitive lines. Maize inbred lines and hybrids were also evaluated for tolerance to high temperature under well-watered condition through field observations following the occurrence of major heat events. Maize inbred lines of distinct heat tolerance phenotype were identifies. Furthermore, genetic and phenotypic analysis showed that maize hybrids made from inbred lines with superior heat tolerance inherited an enhanced tolerance to elevated temperatures. The tolerant germplasm accessions like those identified in this study are essential materials for breeding drought and/or heat tolerance maize hybrids. Study for the potential use of such materials to produce maize hybrids that are able to alleviate the negative impacts of drought and heat stress on the growth and development of maize plants is underway.