Nosema ceranae can cause major problems, such as immune suppression, gut epithelial cell degeneration, reduced honeybee lifespan, or suddenly colony collapse. As a novel approach in therapy, we hypothesize the stable gastric pentadecapeptide BPC 157 in honeybee therapy, to control N. ceranae invasions in apiary conditions: BPC 157 treated sugar syrup (0.25 L sugar syrup supplemented with 0.1 μg/ml BPC 157), as well as the pure sugar syrup (0.25 L sugar syrup; control), was administered to honeybee colonies in feeders situated under the roof of the hives, during 21 consecutive days, at the end of beekeeping season. The strength of honeybee colonies was increased 20 and 30 days after initial feeding with BPC 157 supplement (Day 1, 36.100 ± 698; Day 20, 64.860 ± 468; Day 30, 53.214 ± 312 estimated number of honeybees), in field conditions. The similar successful outcome occurs with the N. ceranae spore loads counted in the homogenates of sampled adult honeybees (Day 1, 6.286 ± 2.336; Day 20, 3.753 ± 1.835; Day 30, 2.005 ± 1.534 million spores/bee). Accordingly, with the noted increased strength of the colonies fed with sugar syrup supplemented with BPC 157, the number of N. ceranae spores per honeybee gradually decreased as well. Besides, honeybees infected with N. ceranae fed with sugar syrup exhibited severe damage of midgut wall layers and epithelial cells. By contrast, in honeybees infected with N. ceranae fed with sugar syrup supplemented with BPC 157, all damages were markedly attenuated, damages of the outer muscular coat, in particular. In conclusion, the results of the first field trial on diseased honeybee colonies with BPC 157 indicate significant therapeutic effects with the used oral therapy with BPC 157 supplementation.