Synthetic lines have been developed in hot climate countries over the last few decades through selection for specific goals such as APRI rabbits, and depending on their specialisation. These lines perform better than the standard of the original breeds, and contemporary production tends to rely on them. The aim of the study was to identify and explain genetic parameters in synthetic maternal line (APRI rabbits) under Egyptian conditions. The Derivative Free Restricted Maximum Likelihood Animal Model (MTDFREML) was used to assess data on body weights (BW) at 4, 8, and 12 weeks, also daily gains (DG) at 4-8, 8-12 and 4-12 weeks. Highest heritability (h²) estimate for BW was at 4 weeks (0.10), while the lowest estimate was at 12 weeks (0.03). The highest estimate (0.08) was for h² of DG at 4-8 weeks, while the lowest estimate was for DG at 8-12 weeks (0.02). All genetic correlations (r_g) between BW at different ages were moderate to high and positive. Estimates of r_g for DG ranged from low to high and were positive, with the exception of (-0.84) between 4-8 and 8-12 weeks. BW and DG at different intervals had significance and the highest was value in the first parity. BW and DG were significantly different in different seasons (P <0.05), with the highest value in autumn. Litter size at birth (LSB) caused significant changes in BW (P<0.05). Moreover, LSB had a significant impact on DG at 8-12 and 4-12 weeks, but not at 4-8 weeks.