CM186, a Hf containing nickel-base superalloy is an attractive alloy, in terms of castability and thus manufacturing costs, for aero engine and land based gas turbine applications. Mechanical property and coating characterisation studies of this alloy are sparse, whilst thermo-mechanical fatigue (TMF) data do not exist in the literature.In service however, engine components experience severe cyclic thermal gradients and mechanical loads and as a consequence, TMF is a major lifing factor. This study investigates the TMF behaviour of single crystal and directionally solidified CM186 alloy and the effect of a silicon modified al&de coating, Sermalloy 15 15, on the TMF lives. Strain controlled TMF tests on coated and uncoated samples are carried out with an out-of-phase 180' difference between mechanical strain and temperature at 3 different strain ranges. In-situ monitoring of microcrack initiation and propagation and post-mortem fiactographic analysis are implemented to understand the damage mechanisms and coating performance.