A well-established activity in Greece and other Mediterranean countries is sheep farming. Karagouniko and Chios sheep are promising breeds and targets for the reproductive physiologist’s attention. Under this context, part of the reproductive physiology of Karagouniko and Chios was investigated, taking into account the environment. Specifically, four time periods were considered; April-June (Long days, increasing photoperiod length), July-September (Long days, decreasing photoperiod length), October-December (Short days, decreasing photoperiod length), and January-March (Short days, increasing photoperiod length). The effect of the period on the concentration of the testosterone (main male hormone) in rams of the breeds above was studied, by using repeated measures analysis of variance, also taking into account the environmental variables air temperature, relative humidity, sunshine, rainfall, and photoperiod, in the Artificial Insemination Center of Karditsa (39°21’18’’N, 21°54’19’’E), Greece. The lowering of photoperiod from April-June to July-September (long days) and afterward, even more to October-December (short days) coincided with a progressive increase of testosterone in both breeds. Photoperiod seems to have a major role in the concentration of Karagouniko and Chios breeds' testosterone compared to the other environmental variables. When considering the whole experimental period, Chios sheep had significantly higher (P < 0.05) testosterone (1.95 ng/ml) than the Karagouniko one (1.55 ng/ml). Our findings could contribute towards the more rational exploitation of the examined sheep breeds.