In this paper, we develop noninformative priors for the log-normal distributions when the parameter of interest is the common mean. We developed Jeffreys` prior, the reference priors and the first order matching priors. It turns out that the reference priors and Jeffreys` prior do not satisfy a first order matching criterion, and Jeffreys` prior, the reference prior and the first order matching prior are different. Some simulation study is performed and a real example is given.