Abstract Temperature is one of the key abiotic factors that determine the proper functioning, growth and development of plants. Variation in temperature will have impacts in growth and yield processes and eventually on the performance of plants. Germination rates will impact on the performance of crops as they will determine stand uniformity as well as give the crop an advantage over weeds. The objective of this study was to quantify the effect of four air temperature levels (day/night, 28oC/18oC, 32oC/22oC, 36oC/26oC, 38oC/28oC) on the germination rates of three grain amaranth species (Amaranthus tricolor, Amaranthus cruentus, and Amaranthus hypochondriacus). Experiments were conducted in a replicated randomized block design in four controlled environment growth chambers. All the plants were subjected to the photoperiod (12 h) and thermoperiod. The temperature was gradually ramped to the set points. Growth chamber and soil temperatures were monitored throughout the experiment and germinated seeds were counted on the 4th, 5th, 6th, 8th, and 10th day after sowing. Results showed that there was significant variation in germination rates and percentages among the species. Amaranthus cruentus had higher germination percentage and faster rates of germination across all temperatures, particularly at both cooler and higher temperatures, compared to other two species. This shows that there is genetic variation among the three grain amaranth species in response to temperature which should be exploited in the breeding programs.