The aim of the study was to assess the suitability of egg specific gravity (ESG) as an accompanying trait in estimation of the birds’ breeding value for hatchability. The study involved 3 generations of performance recorded laying hens Rhode Island White (RIW) and Rhode Island Red (RIR). The breeding merit for number of chicks hatched from eggs laid (NCH) was estimated with three different model variants which differed with regard to the information accounted for: 1. all the standard information plus post factum hatchability record and ESG, 2. no post factum hatchability data on the last generation but ESG present, and 3. no hatchability data on last generation nor ESG. In both lines a high positive correlation between the egg specific gravity and hatchability was observed (0.47 to 0.66). In RIR, when ESG was included in the left-hand-side, a significantly higher concordance of birds’ NCH breeding value ranking between 2. and 1. than between 3. and 1. were observed.