It is obvious that heat exchanger performance is highly related with fin material thermal conductivity. In this paper 3-D numerical simulations were performed for conjugate heat transfer and fluid flow characteristics of fin and tube heat exchanger. The effects of the fin materials interacting with five factors: Reynolds (Re) number, fin pitch (FP), fin thickness (FT), tube diameter (TD) and fin length (FL) were examined. However, high thermal conductivity materials may not be suitable under some operating conditions such as food processing. It is found that thermal conductivity of the material slightly increases the effect of the Re number on Nusselt (Nu) number and the thermal conductivity is becoming very important parameter while investigating the effect of tube diameter on Nu number. Similarly the effect of fin length and fin thickness is also affected by fin material. A new correlation is proposed to predict Nu number includes the effect of all these parameters.