© 2018 Institute of Navigation. All rights reserved. To evaluate impacts of ionospheric scintillations on integrity monitors of GAST-D (Ground-Based Augmentation System (GBAS) Approach Service Type D), responses of test statistics of four GAST-D integrity monitors including the cycle-slip monitor, dual-solution pseudorange ionospheric gradient monitoring algorithm (DSIGMA range-domain), CCD monitor and ISGM, that are relevant to the ionospheric activities are studied. Data used are the GBAS data collected by an experimental prototype of GAST-D developed by Electronic Navigation Research Institute (ENRI) and installed at the New Ishigaki Airport, Japan (24.3ºN, 124.2ºE, 19.6ºN magnetic), and ionospheric scintillation data observed near the airport. The data obtained on 30 days of strong scintillations from August 2014 to March 2015 are used. The test statistics of the four integrity monitors are successfully modeled as a function of the amplitude scintillation index (S4). With these models, probabilities of monitor trips with the existence of amplitude scintillations can be evaluated, if the integrity monitor thresholds are provided based on the integrity monitor algorithms and risk allocation strategies. Or the integrity monitor thresholds can be determined, if the tolerable probabilities of monitor trips are provided. It is also important to consider the inter-relation between the monitors, as they may not be independent. Once the inter-relation between the monitors in terms of response to the amplitude scintillation, it would be ready to run extensive GAST-D simulations to evaluate its performance in the low magnetic latitude regions where the scintillation activities are high.