Expanding utilization of conventional fish feed ingredients by man and fish feed industries has necessitated consideration of cheaper and locally available alternatives. A 70-day feeding trial was conducted to assess the effect of substituting graded levels of sundried flamboyant (Delonix regia) leaf meal (SFLM) for groundnut cake on growth and feed utilization of 240 Clarias gariepinus fingerlings at six substitution levels of 0 (control), 20, 40, 60, 80 and 100% in 12 plastic aquaria (50 × 40 × 40 cm). Each dietary treatment was randomly assigned in two replicates each to the aquaria making 12 treatment units and each aquarium had 20 fish. SFLM supplemented diets and fish carcass were proximately analyzed using standard procedures. Mean weight gain (MWG), specific growth rate (SGR) and feed conversion ratio (FCR) were determined. Data obtained were analyzed using descriptive statistics and ANOVA at p ≤ 0.05. Crude protein was highest (68.89%) in fish fed with diet 4, least (64.61%) in fish fed with diet 1 (control) and significantly (p < 0.05) exceeded 60.54% of the pre-treatment fish carcass. Fish fed with diet 3 had significantly (p < 0.05) higher values of MWG (11.73 g), SGR (2.13%/day) and superior FCR (0.451) above which growth and feed utilization indices progressively declined with increase in the substitution level of SFLM. This study revealed that 40% substitution level of the SFLM resulted in the best growth and feed utilization in C. gariepinus. The study demonstrated the considerable potential of flamboyant leaf meal as an alternative protein source, therefore other processing methods are recommended to increase its utilization, reduce feed cost and maximize aquaculture profitability.