Various thermo mechanical processes have been studied to improve the mechanical properties of 18Ni-Co-Mo steels. In this work, the effect of interpass aneal time on the mechanical properties of the 18Ni-Co-Mo steel was investigated, using the rolling experiments. Hot rolling process was performed in two passes. The reduction of area was 30% in the first pass at 1100 °C. After first pass specimens were air cooled to second pass temperature (900°C) and held for various interpass time (2 sec, 5 min and 10 min). The second pass was performed at 900°C for 20% reduction of area. After that, the specimens were directly water quenched to retain the microstructure present at the second pass. Tensile and charpy tests samples were machined from hot rolled specimens. The results showed that grain size was decreased significantly at these conditions by increasing the interpass time from 2 sec to 5 min. This was attributed to the static recrystallization. With an increase in interpass time to 5 min, tensile strength was increased, without significant change in charpy impact energy. Increasing the interpass time from 5 to 10 min, increased austenite grain size. This was attributed to the grain growth. The results indicated that the interpass time of 5 min can be considered to obtain the maximum tensile strength.