The level of reproductive efficiency is predominantly related to the values of the basic parameters of sow fertility, such as weaning-to-estrus interval, farrowing rate (%) and litter size. These values, however, were frequently reduced, in the warmer part of the year. This phenomenon is defined as seasonal sows infertility. This paper review the basic factors of sows seasonal infertility, their mechanisms of action, as well as the possibilities of practical solutions of this significant problem in pig reproduction.