The purpose of this paper is to apply conditional Ulam stability, developed by Popa, Ra\c{s}a, and Viorel in 2018, to the von Bertalanffy growth model $\frac{dw}{dt} = aw^{\frac{2}{3}}-bw$, where $w$ denotes mass and $a>0$ and $b>0$ are the coefficients of anabolism and catabolism, respectively.
This study finds an Ulam constant and suggests that the constant is biologically meaningful.
To explain the results, numerical simulations are performed.