Background: Therapeutic diets for infantile colic lack evidence. In breastfed infants, avoiding “windy” foods by the breastfeeding mother is common. Aim: To examine the effects of a maternal low-FODMAP (Fermentable, Oligosaccharides, Disaccharides, Monosaccharides, And Polyols) diet compared to a typical-Australian diet on infant crying-fussing durations of infants with colic in a randomised, double-blind, crossover feeding study. Methods: Between 2014 and 2016 exclusively breastfed infants aged ≤9 weeks meeting Wessel criteria for colic were recruited. Mothers were provided a 10-day low-FODMAP or typical-Australian diet, then alternated without washout. Infants without colic (controls) were observed prospectively and mothers remained on habitual diet. Infant crying-fussing durations were captured using a Barr Diary. Measures of maternal psychological status and samples of breast milk and infant faeces were collected. Results: Mean crying-fussing durations were 91 min/d in seven controls compared with 269 min/d in 13 colicky infants (P < 0.0001), which fell by median 32% during the low-FODMAP diet compared with 20% during the typical-Australian diet (P = 0.03), confirmed by a two-way mixed-model analyses-of-variance (ƞp 2 = 0.719; P = 0.049) with no order effect. In breast milk, lactose concentrations remained stable and other known dietary FODMAPs were not detected. Changes in infant faecal calprotectin were similar between diets and groups, and faecal pH did not change. Median maternal anxiety and stress fell with the typical-Australian diet (P < 0.01), but remained stable on the low-FODMAP diet. Conclusions: Maternal low-FODMAP diet was associated with enhanced reduction in crying-fussing durations of infants with colic. This was not related to changes in maternal psychological status, gross changes in breast milk or infant faeces. Mechanisms require elucidation. Trial Registration Australian New Zealand Clinical Trials Registry (ANZCTR): 12616000512426 - anzctr.org.au.