Objective: The aim of this study was to determine the pathogens causing lower respiratory tract infections (RTI) among immunocompromised patients and their antimicrobial susceptibility pattern. Materials and Methods: It was a cross-sectional study conducted at Pathology Department, Allama Iqbal Medical College, Lahore, from July 2015 to December 2015. Early morning deeply coughed out sputum samples from patients having productive cough and fever admitted in the oncology ward of Jinnah Hospital, Lahore, belonging to any age group, any gender, and on chemotherapy were included. Salivary specimens and specimens from the same patient during the same episode of illness were excluded from the study. These sputum samples were cultured on Blood agar, MacConkey agar and Chocolate agar using standard microbiological techniques & antibiotic susceptibility pattern were determined using Modified Kirby Baur disc diffusion method following CLSI guidelines 2015. Results: During study duration, a total of 100 sputum specimens from immunocompromised cancer patients were received. Out of total 100 samples, 70% were culture positive, 30% samples yielded normal throat flora. Out of 70 culture positive, 55(79%) were Gram negatives and 15(21%) were Gram positives. Among Gram positives, Streptococcus species were yielded from 11(73%) specimens. Among Gram negatives, Klebsiella species were yielded from 20(36%) specimens. All Grampositive isolates were susceptible to linezolid and vancomycin. All Gram-negative isolates were susceptible to amikacin and 88% Gramnegative isolates were susceptible to imipenem. Conclusion: Gram-negative rods usually don't cause respiratory tract infections in normal healthy individuals. But in immunocompromised patients like cancer patients, they become a serious concern. As in our study, Gram-negative rods were responsible for around 79% of the respiratory tract infections.