The scientists claimed the gas increased the purity of the stem cells.
Small amounts of hydrogen sulphide are made by the body.
It is also produced by bacteria and is toxic in large quantities.
Therapy A group in China has already reported using the gas to enhance the survival of mesenchymal stem cells taken from the bone marrow of rats.
Researchers at the Nippon Dental University were investigating stem cells from dental pulp - the bit in the middle of the tooth.
They said using the gas increased the proportion of stem cells which were converted to liver cells when used alongside other chemicals. The idea is that liver cells produced from stem cells could be used to repair the organ if it was damaged.
Dr Ken Yaegaki, from Nippon Dental University in Japan, said: "High purity means there are less 'wrong cells' that are being differentiated to other tissues, or remaining as stem cells."
One of the concerns with dental pulp as a source of stem cells is the number that can be harvested.
However, the study did not say how many cells were actually produced.
Prof Chris Mason, a specialist in regenerative medicine at University College London, said: "It would be interesting to see how hydrogen sulphide works with other cells types."