The objectives of this study were to detect the relationship between body mass index (BMI) and body condition score (BCS) in Pelibuey ewes to predict BMI based on well-known BCS estimation. The body weight (BW), withers height, (WH), body length (BL) and BCS were determined in 402 ewes. The BMI was calculated as: BMI = (BW (kg)/WH (m)/ BL (m))/10. Relationships were estimated by means of regression models using PROC REG of the SAS. The BMI and the BCS showed a high relationship; correlation coefficient (r) of 0.80 (P<0.001). The linear regression for BMI prediction was as followed: BMI (kg/m2) = 8.38 (±0.189***) + 1.70 (±0.064***) × BCS (R2 = 0.65, MSE: 2.56; RMSE: 1.60; P <.0001 and n = 402). The BMI could be used as an indicator of the degree of obesity in non-pregnant and non-lactating Pelibuey ewes under field conditions.