This invention relates to a temperature control indicator unit comprising a substrate having supported thereon (a) microcapsules enclosing a hydrophobic organic compound possessing an arbitrarily selected melting point, (b) a methine dye and (c) an oxidizing material. More particularly, a unit made by combining an irreversibly color-developing methine dye and an oxidizing material with microcapsules enclosing a hydrophobic organic compound possessing a predetermined melting point and supporting them on a substrate is used for temperature control purposes. A suitable measure is taken, preferably at or below the desired control temperature, to break at least a part of the microcapsules of the unit and thereby produce fissures or the like in the microcapsule membrane. Then, the unit is stored or transported together with an article to be placed under temperature control. As a result, if the article is exposed to temperatures exceeding the desired control temperature, the non-volatile organic compound present in the broken microcapsules melts and diffuses out. This brings the methine dye into contact with the oxidizing material present in proximity thereto and causes an irreversible color development of the methine dye. Thus, the occurrence of abnormal temperature control conditions can be detected by observing such color development.