Simple SummaryAccess to antibiotics online endangers its responsible use, increasing the risk of bacterial resistance emergence. The objective of this study was to assess the possibility of purchasing antibiotics for veterinary use on the internet, evaluating the availability of those classified as highest priority critically important antimicrobials (HP-CIA), and if a prescription is required. The Google and Bing search engines and both simple and complex search strings in Spanish and in English were used. The simple search string was “buy veterinary antibiotics”. Complex searches used wildcards and specific syntax. The searches carried out in Spanish revealed that 50% of websites operated in South America and 65% of websites did not require a valid prescription. For the searches in English, 57% of websites operated in the United States of America (USA) and 55% of them did not require a prescription. Our study shows that veterinary antibiotics are easily available for purchase online without a prescription.Antibiotics are essential medicines against infectious diseases in both humans and animals. An inappropriate use of antibiotics can impair animal health and enhance the risk of bacterial resistance, as well as its transfer from animals to humans. The objective of this study was to assess the possibility of purchasing antibiotics for veterinary use on the internet, to evaluate if a prescription is required, and to determine the availability of drugs classified as the highest priority critically important antimicrobials (HP-CIA). The Google and Bing search engines and both simple and complex search strings in Spanish and in English were used. The simple search string was “buy veterinary antibiotics”. Complex searches used wildcards and specific syntax. The searches carried out in Spanish revealed that 50% of websites operated in South America, and 65% of websites did not require a valid prescription. Fluoroquinolones were offered in 84% of these websites (45% without prescription), macrolides were offered in 63% of these websites (43% without prescription), and 3rd– and 4th–generation cephalosporins in 54% of these websites (38% without prescription). For the searches in English, 57% of these websites operated in the United States of America (USA), and 55% of them did not require a prescription. Fluoroquinolones were offered in 79% of these websites (49% without prescription), macrolides were offered in 72% of these websites (45% without prescription), and 3rd– and 4th–generation cephalosporins were offered in 49% of these websites (27% without prescription). Therefore, it is easy to illegally access antibiotics via the internet.