iGABASnFR2 is a genetically encoded fluorescent sensor designed for in vivo detection of GABA (γ-aminobutyric acid), generated by mutagenesis of iGABASnFR1, containing in addition three mutations (S99A, F102Y, F104Y) in the GABA-binding Pf622 protein part of the sensor and a single mutation (L178S) in the circularly permuted sfGFP part of the sensor. These changes result in iGABASnFR2 having improved sensitivity and faster kinetics compared to iGABASnFR1 (DOI:10.7554/eLife.108319.1).