COVID-19 caused by SARS-CoV-2 is an emerging severe acute respiratory disease affecting global human health. In this study, a large-scale serological survey of antibodies against SARS-CoV-2 in dogs and cats was conducted during the 1 and 2 waves of COVID-19 outbreaks in Thailand, from April to December 2020. A total of 3,215 serum samples were collected from dogs (n = 2,102) and cats (n = 1,113) living in Bangkok and in the vicinities. Serum samples were tested for SARS-CoV-2 antibodies by using an indirect multispecies enzyme-linked immunosorbent assay (ELISA). Positive and suspected samples were additionally tested for neutralizing antibodies by the surrogate virus neutralization test (sVNT). The indirect ELISA results showed that 1.66% (35/2103) of dogs and 0.36% (4/1112) of cats were positive for SARS-CoV-2 antibodies. The sVNT results showed that all ELISA-positive and suspected samples were negative for neutralizing antibodies. Positive serum samples (35 dogs and 4 cats) were obtained from clinically healthy animals and animals with mild respiratory signs aged <1-13 years living in Bangkok and Samutprakarn Provinces. In summary, a serological survey revealed evidence of anti-N-IgG antibodies suggesting SARS-CoV-2 exposure in both dogs and cats during the 1 and 2 COVID-19 outbreaks in Thailand. This article is protected by copyright. All rights reserved.