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The effect of the entomopathogenic fungus <i>Beauveria bassiana</i> (BB-12) on the biological characteristics of <i>Tamarixia radiata</i> parasitizing <i>Diaphorina citri</i> was studied under laboratory conditions. Twenty 3rd–5th instar nymphs were exposed to a single already-mated female parasitoid (1 day old) and removed after 24 h. Subsequently, the nymphs were sprayed at 1, 24 and 48 h post-exposure with 1 × 10⁸ conidial mL⁻¹ suspension. The percentage of parasitism recorded was 22%, 35% and 41% at 1, 24 and 48 h, respectively. The emergence rate varied between 28%, 51% and 49% at 1, 24 and 48 h, respectively. In a subsequent experiment, nymphs of <i>D. citri</i> were sprayed with 1 × 10⁸ conidial mL⁻¹ suspension and then exposed to <i>T. radiata</i> at 1, 24 and 48 h post-spraying to allow for parasitism to occur. The percentage of parasitism recorded was 18%, 27% and 28% at 1, 24 and 48 h, respectively, significantly lower than the parasitism rate recorded in the control (48%). The percentage of emergence varied between 24%, 44% and 45% at 1, 24 and 48 h, respectively. In both experiments, no significant difference was observed in the pre-adult duration (days) and the sex ratio of F1 generation. Meanwhile, significant differences were observed in the longevity of the F1 generation of females and males of <i>T. radiata</i> in a treatment consisting of spraying the fungal suspension and the control. Overall, the findings of the current study revealed a negative interaction between <i>T. radiata</i> and <i>B. bassiana</i> in controlling <i>D. citri</i> nymphs. This outcome is believed to be a result of the antagonistic effects of <i>B. bassiana</i> on the developmental process of the pre-adult stages of the parasitoid. However, our results also show that with a properly timed application (allowing parasitism to occur over an extended period of time before the application of the fungus), <i>T. radiata</i> could potentially be used in combination with <i>B. bassiana</i> for the successful biological control of <i>D. citri</i>. This should be carried out in order to minimize the potentially negative interactions between these two biological agents.