The length-weight relationship and the relative condition factor of yellowfin tuna Thunnus albacares collected on the Parangipettai coast, southeast coast of India was studied. Logarithmic equations did not show any significant difference in the regression coefficient for males, females, and indeterminates of T. albacares. The exponent ‘b’ values were less than 3 (b > 3) and expressed as 2.78 for males, 2.82 for females, and 1.79 for indeterminates. The relative condition factor (Kn) decreased with the increasing of fork length, which showed seasonal fluctuations during the study period. The Kn values were found to be higher in the post-monsoon than in pre-monsoon season. The Kn value obtained from the present study is 1, which indicates a good health condition of fish, while the values less than 1 predict an unhealthy condition of fish. The Kn values fluctuated between 0.97 and 1.60 for both sexes, and it is clearly evident that the health condition of T. albacares caught along the Parangipettai coast is good and the site is a good environment for their survival.