Folates (B vitamins) are essential for the proper function of many bodily processes. Although a rich natural source are vegetables, the literature lacks data on the effect of the pre-treatment and freezing technologies used in vegetable processing and frozen storage time on the folate content in these materials. Moreover, since folates are very unstable nutrients, the amount available in processed and stored foods can be significantly lower than in raw products. In tested vegetables (green beans, yellow beans, peas, cauliflower, broccoli and spinach), one folate form was identified, 5-methyltetrahydrofolate (5-CH₃-H₄folate). It was observed that pre-treatment and freezing technology significantly (p < 0.05) decreased 5-CH₃-H₄folate content only in vegetables with the largest degree of fragmentation (cut and briquetted spinach) and the smallest size (peas). In all analyzed samples, the 5-CH₃-H₄folate content decreased with the time of frozen storage. In frozen cauliflower, the 5-CH₃-H₄folate loss exceeded 95 % compared to the fresh product just after the third month of frozen storage. Meanwhile, in green and yellow beans, significant 5-CH₃-H₄folate losses (at the level of 75 % and 95 %, respectively) were observed no earlier than after the 9th month of frozen storage.