Nimonic type heat-resisting alloys have increased Co, Mo and Al+Ti content for the improvement of high temperature properties, at the expense of the forgeability. The principal cause for the loss of forgeability is due to the increase of Al+Ti content. Therefore, in the present paper, the effect of Al+Ti content on the forgeability of Nimonic-100 type alloys was investigated, and also next place, the age-hardening property, the oxidation resisting property and the metallographical structure of the alloys were examined. The results obtained were as follows: (1) Under the present experimental condition, the limit of possible hot-working of Nimonic 100 type alloys is on the line linking a point of about 4.5%Al and 0%Ti with a point of 0%Al and about 5%Ti, when the Al content is choosen as the coordinate and Ti as the abscissa. (2) The Vickers-hardness on the above boundary line is about 230∼260 in the case of solution-treated alloys. (3) The deformation resistance at 1100°C on the line is about 40∼45 kg/mm². (4) The time required to reach maximum hardness in age-hardening at 900°C of the alloys is about 8∼30 hrs, and the amount of the softening is small in aging below 500 hrs. (5) From the result of age hardening test of the specimens containing a definite amount of Al+Ti, it was found that Ti contributed in age-hardening more than Al. (6) The constitutional diagram of the alloys solution-treated at 1150°C for 15 hrs was determined. (7) Al is effective for the improvement of oxidation resistance, but Ti has a detrimental effect on the contrary.