A study was conducted to examine the persistence and decay of web citations in theses and dissertations available at the Sokoine National Agricultural Library. Specifically, the study assessed the accessibility status of cited URLs, identified error messages and top level domains of inaccessible URLs, and calculated the half-life of web citations. Eighty-three theses and dissertations that were dated between 2007 and 2011 were stratified according to their years of publication and randomly selected for the study. These gave a total of 15,468 citations of which 1,487 (9.6%) were web citations. The findings show that a total of 862 (58%) web citations were inaccessible. The "404 File Not Found" error message was the most (92.7%) encountered and the ".com" domain had the greatest number (28.2%) of missing URLs. The average half-life for the URLs cited in theses and dissertations was 2.5 years. The study findings therefore indicate that many web resources cited in theses and dissertations available at SNAL had disappeared from their original locations. Collaborative efforts are thus required from various stakeholders in order to reduce the problem of URL decay.