The fatigue crack growth (FCG) behavior of a newly developed Ni-Co-base superalloy TMW-4M3 has been investigated in this study. Experiment was carried out in laboratory air with compact-tension specimen. The effects of temperature (400, 650, and 725 degrees C) and load ratio (0.05 and 0.5) on crack growth rate were studied in the Paris regime. The results revealed that the crack growth rate increased with increasing temperature under a given load ratio. The influence of load ratio on crack growth rate was pronounced, especially at higher temperature and low stress intensity factor range. Fractographic observations showed that fracture mode was transgranular at 400 degrees C, mixed transgranular and intergranular at 650 degrees C, and predominantly intergranular at 725 degrees C. The possible explanations for the crack growth behavior were discussed based on the degradation of mechanical properties and the oxidation assisted crack growth, as well as the crack closure effect. A comparison of FCG rate was also made between TMW-4M3 and the commercial superalloy U720Li.