In 2017, Philadelphia enacted a $0.015 per ounce excise tax on SBs that covered both sugar-sweetened beverages and artificially-sweetened beverages, which reduced purchasing and consumption. This study assessed whether the tax also changed beverage advertising or stocking practices that could influence consumer behavior among stores in Philadelphia, Baltimore, and Philadelphia-adjacent counties not subject to the tax. Using a longitudinal difference-in-differences approach, beverage advertising and availability changes were evaluated from 4-month pretax to 6-, 12-, and 24-month post-implementation in small independent stores in Philadelphia (n=34) and Philadelphia-adjacent counties (n=38) versus Baltimore (n=43), a demographically similar city without a tax. Mixed effects models tested whether beverage advertising/availability increased in Philadelphia and surrounding counties after implementation versus Baltimore, included store-level random intercepts, and were stratified by beverage tax status, type, size, and store ZIP code income. Data were collected from 2016 to 2018, and analyses were performed in 2022–2023. SB advertising increased post-tax in Philadelphia (6 months= +1.04 advertisements/store [95% CI=0.27, 1.80]; 12 months= +1.54 [95% CI=0.57, 2.52]; 24 months= +0.91 [95% CI=0.09, 1.72]) relative to Baltimore. This was driven by increased advertising of sweetened beverages in low-income ZIP codes. Marketing of SBs increased significantly in Philadelphia-adjacent counties relative to Baltimore. Although SB availability in Philadelphia did not change, it increased in surrounding county stores (6 months= +0.20 [95% CI=0.15, 0.25]; 12 months= +0.08 [95% CI=0.03, 0.12]) relative to Baltimore. Marketing of SBs, especially in low-income neighborhoods and in surrounding counties, increased following Philadelphia’s beverage tax among small, independent retailers. These increases in advertising might have dampened the tax’s effect on purchasing behaviors, although estimated effects on sales remained large.