We describe one-pot synthesis of highly luminescent nanocrystals (NCs) of silver indium sulfide (AIS) by simply heating low-toxic Ag and In precursors in the solution. Our AIS NCs with the average size of similar to 2.3 nm showed an optimal value of absolute photoluminescence quantum yield (PL-QY) of similar to 60%. Moreover, such high PL-QY values of AIS NCs were adequately stable even after gently storing at room temperature for over 21 months.