Heritability of and genetic correlation of two traits, weight and length,. measured in Oreochromis niloiicus (1150 records) were estimated using MTDFREML programme. The model included fixed effect of line (four lines: Giza (G)} Fouky (F), Mariut (M) and Nag Hamady (N)). Besides, the model included the effects of individual (fish), sire and dam as random effects. The results of h2 for the two traits were 0,99, 0,87, respectively. The genetic correlation between the two tested traits was 0.91. Ignoring line effect, the same previous model was used to estimate heritability and genetic correlation for the two studied traits for each line. Line N recorded the best estimate of h2 for weight (1.0), whilst line M had the highest estimate of/^ for length (0.97). The estimated genetic correlation (0.98) for line M was higher than that of the other experimental lines.