We previously found that flowering of Arabidopsis was suppressed by near‐null magnetic field, which was related to the modification of cryptochrome. To disclose the physiological mechanism of this effect, we detected gibberellin (GA) levels and expressions of GA biosynthetic and signaling genes in wild type Arabidopsis plants and cryptochrome double mutant, cry1/cry2, grown in near‐null magnetic field. We found that levels of GA4, GA9, GA34, and GA51 in wild type plants in near‐null magnetic field were significantly decreased compared with local geomagnetic field controls. However, GA levels in cry1/cry2 mutants in near‐null magnetic field were similar to controls. Expressions of three GA20‐oxidase (GA20ox) genes (GA20ox1, GA20ox2, and GA20ox3) and four GA3‐oxidase (GA3ox) genes (GA3ox1, GA3ox2, GA3ox3, and GA3ox4) in wild type plants in near‐null magnetic field were significantly reduced compared with controls, while expressions of GA20ox4, GA20ox5, GA2‐oxidase (GA2ox) genes, and GA signaling‐related genes in wild type plants in near‐null magnetic field were not significantly different from controls. In contrast, expressions of all the detected GA biosynthetic and signaling genes in cry1/cry2 mutants were not affected by near‐null magnetic field. Moreover, transcriptions of flowering‐related genes, LFY and SOC1, in wild type plants were downregulated by near‐null magnetic field, while they were not affected by near‐null magnetic field in cry1/cry2 mutants. Our results suggest that the effect of near‐null magnetic field on Arabidopsis flowering is GA‐related, which is caused by cryptochrome‐involved suppression of GA biosynthesis. Bioelectromagnetics. 38:1–10, 2017. © 2016 Wiley Periodicals, Inc.