Although evidence from high-income countries suggests that mass media campaigns can increase knowledge of tobacco harms and encourage smoking cessation, there is little evidence of this from developing countries, particularly related to campaigns that seek to increase support for smoke-free places and laws. Two campaigns that ran in São Paulo, Brazil during implementation of a smoke-free law in São Paulo were evaluated to assess their effectiveness in changing attitudes and creating support for the law. The campaigns were evaluated through street-intercept surveys conducted in early July and late August in São Paulo (Ns= 603; 615). Findings reveal that mass communications can generate support for smoke-free laws and underscore the importance of running campaigns that are both well-funded and that use harder-hitting, more graphic messages.