Background <p>The purpose of this study was to evaluate the utility of fluorine-18-fibroblast activation protein inhibitor (¹⁸F-FAPI) PET/CT for detecting brain metastasis (BM) in different pathological types of lung cancer using craniocerebral MRI as the standard.</p> Methods <p>From December 2020 to October 2021, patients with pathologically confirmed lung cancer and suspected BM were prospectively enrolled and underwent paired ¹⁸F-FAPI PET/CT and MRI. The number of BMs and maximum tumor diameter were measured by MRI. The maximum and peak standardized uptake values (SUVmax and SUVpeak, respectively) and tumor-to-background ratio (TBR) on ¹⁸F‐FAPI PET/CT in BMs were evaluated.</p> Results <p>A total of 76 BM lesions from 18 patients (11 males and 7 females) were evaluated. Among these, 23 lesions were detected by ¹⁸F-FAPI PET/CT. The detection rate of BM in adenocarcinoma was 48.28%, which was significantly higher than that in large cell carcinoma (16.67%, <i>P</i> = 0.016) and small cell carcinoma (0%, <i>P</i> = 0.009), but showed no significant difference from that in squamous carcinoma (35.71%, <i>P</i> = 0.437). The detection rate in squamous carcinoma was significantly higher than that in small cell carcinoma (<i>P</i> = 0.043), while no significant differences were observed between large cell carcinoma and small cell carcinoma (<i>P</i> = 0.183), or between large cell carcinoma and squamous carcinoma (<i>P</i> = 0.191).</p> Conclusions <p>This study revealed differences in the detection rates of BM in lung cancer types by ¹⁸F-FAPI PET/CT, with the highest and lowest detection rates in adenocarcinoma and small cell carcinoma, respectively, which may be valuable for predicting the prognosis of lung cancer patients with BM.</p> Trial registration <p>Institutional review board approval NO. SDZLEC2021-112-02.</p>