Growth improvement is often the first objective of selective breeding programs in fish. This study aimed to investigate effects of broodstock age and sizes individually selected based on two cut-off values (5% and 25 % of the normal distribution of the G1 population?s weight) on offspring growth of climbing perch (Anabas estudineus) from fry to grow-out stages. Climbing perch (?square-head? strain) fry artificially produced from two selected G1 parents (G2-S1 and G2-S2, respectively) and from the first generation (G1-0) were compared growth and survival rates with the one from non-selected G1 parents (G2-NS) in three experiments, corresponding to two nursing and grow-out stages. In the first experiment, fry fish were randomly stocked in 1-m³ tanks with 4 replicates at the density of 3000 fish/tank. Fish were fed by live food (rotifer, moina, red worm) combined with commercial feed (42% protein). After 21 days, length of fish in 2 selected groups (2.51±0.06 cm and 2.42±0.09 cm) was insignificantly higher that offspring in the control and treatment G1-0 (2.41±0.02 cm and 2.37±0.06 cm, respectively). However,fish weight in G2-S1 was significantly highest (0.43±0.37^ưg⁾ compared to the other treatments (averaged 0.32 - 0.36 g). Survival rates were not significant among treatments (P>0.05), ranging from 14.0±1.8% to 18.6±3.6%. At fingerling to juvenile stages, fish were reared in 2 m² -hapas (200 fish/hapa) and fed commercial feed containing 42% protein. After 30 days of rearing, growth of fish in G2-S1 was highest (6.5±1.6 cm and 6.3±4.8 g), significantly different from the other treatments (P0,05), ranging 79.8 to 84.9%. Therefore, mass selection of 5% highest weight individuals of the population increases growth rate of squared head climbing perch from fry to juvenile stages. Results of 4-month grow out showed that fish in treatment G2-S1 had the highest growth rate (final weight 126.4±25.2 g), significantly different from the other treatments (80.0 ? 89.3 g). Survival rates were similar among treatments (P>0.05), ranging 82.8 ? 94.8%. Feed conversion ratio was significantly lower in selected groups compared to the control and treatment G1-0. Heritability of growth at grow-out stage was 0.31 for 5% selected group and -0.02 for 25% selected group. Therefore, mass selection of 5% highest weight individuals of the population increases growth rate of climbing perch.