Cystic Fibrosis (CF) is a multi-organ genetic disorder and Transforming Growth Factor (TGF-β1) is a modifier gene which modulates lung pathology in CF. There is great phenotypic variability among CF patients who even have similar genotype. The aim of the present study was to associate the serum levels of TGF-β1 with several clinical phenotypes of CF. The diagnosed cases of CF were recruited and the blood sample was withdrawn at different time points: during exacerbation (n = 26), non-exacerbation (n = 9) and after antibiotic therapy (n = 11). The concentration of the total TGF-β1 in serum was measured with commercial ELISA kit. The ΔF508 mutation was assessed by the Amplification Refractory Mutation System (ARMS-PCR). The levels of TGF-β1 were increased in exacerbation phase (119.89 ± 29.64ng/mL), infection with P. aeruginosa (121.8 ± 28.83ng/mL) and in subjects with ΔF508 mutation (139.2 ± 19.59ng/mL). The levels of TGF-β1 in CF patients with Allergic Bronchopulmonary Aspergillosis (ABPA) (109.97 ± 27.71ng/mL) were decreased as compared to CF patients without ABPA (123.55 ± 30.20ng/mL). It was observed that the serum levels of TGF-β1 were decreased significantly after antibiotic therapy (p < 0.05). The present study has determined that the serum levels of TGF-β1 vary with the type of infections, ΔF508 CFTR mutation, presence of ABPA and response to therapy.