Expressing gratitude can promote generosity (Algoe, Dwyer, Younge, & Oveis, 2020; Grant & Gino, 2010; Williams & Bartlett, 2015), but not all studies have found this to be true (Samek & Longfield, 2019). We look beyond whether a person was thanked or not, and instead consider the quality of the gratitude expression. Theory points to one aspect of a “thank you” that can make it more potent, specifically the extent to which it involves other-praising behavior, and research has found that other-praising gratitude expressions are more effective in promoting relationships than gratitude expressions focused on self-benefits (Algoe, 2012; Algoe, Kurtz, & Hilaire, 2016). We take this work a step further by examining the influences of these two kinds of gratitude expressions on charitable giving. We ran two preregistered field experiments (Ns = 1009 and 847) to examine the question: Compared to self-benefit expressions, do other-praising expressions in thank-you messages increase donor retention and level of future donations? Donors to a large public university were randomly assigned to receive a thank-you call (Study 1) or text message (Study 2) from a student that used either a self-benefit script or an other-praising script. The dependent variables were whether donors made a subsequent gift and whether those gifts were less than, the same as, or more than their previous donation. In both studies, we found a significant advantage of the other-praising script in promoting subsequent giving (although in Study 1 this only occurred when a conversation was had, as opposed to when a voicemail was left). However, we did not find an effect of script type on giving amount in either study. In conclusion, our findings suggest an advantage of other-praising gratitude expressions on whether people give, but not on how much they give. These are the first findings that we are aware of on the effect of these two types of gratitude expressions on people's charitable giving behavior.