Prior research has documented the availability of drugs on many Tor Network websites, with the Internet playing a particularly vital role in the global new psychoactive substances (NPS) market. The primary objective of this research was to document types of NPS for sale on the largest operating Tor site (Agora) over a period of four months. Secondary objectives were to analyze countries and vendors sourcing NPS on Agora. Data from Agora were collected in February and June 2015. The number of total advertisements on Agora increased from 20,742 to 27,431 over the four months, while the number of NPS advertisements increased from 2,205 to 2,271 and the number of vendors increased from 157 to 288. The composition of NPS listings and source countries for NPS advertised on Agora diversified over time. Advertisements for ketamine and unclassified NPS experienced substantial growth, while the availability of phenethylamines decreased. However, phenethylamines remained the most frequently advertised NPS type. China and the U.S. were found to be the top two countries by volume selling NPS on Agora over the fpir months, but the number of countries identified as advertising NPS increased by nearly 43%. The United States housed the most NPS vendors.