Background: Silver nanoparticles (Ag-Nps) and Titanium dioxide nanoparticles (TiO2-Nps) are well-known nanoproducts. Both of them have many industrial applications. Lung is one of the major target organs for prolonged nanoparticles exposure. Objective: This study was designed to investigate and compare the possible histopathological toxic effect of Ag-Nps & TiO2- Nps on lung and which of them is safer for future using. Materials & methods: 54 adult male albino rats were divided into 3 equal groups; GroupI (control group), Group II that subdivided into two subgroups; Subgroup IIa: Ag-Nps group with (100 mg/kg/day) daily for 4 successive weeks and Subgroup IIb recovery group left for 4 weeks without injection, Group III that subdivided into two subgroups; Subgroup IIIa: TiO2-Nps group with (150 mg/kg/day) for 4 successive weeks and Subgroup IIIb recovery group left for 4 weeks without injection. Lung specimens were processed for light and electron microscope and immunohistochemical expression of caspase-3 and CD-68. Morphometric and statistical analysis were performed. Results: Group IIa showed collapsed alveoli, others showed ballooned distension and marked thickening of inter-alveolar septa. Extensive cellular infiltration was detected. Group IIIa showed focal areas of collapsed alveoli and thick inter-alveolar septa. Mild cellular infiltrations were observed. Areas of extravasation were detected in the interstitium. Group IIIb showed signs of improvement which is more than group IIb. Conclusion: exposure to Ag-Nps showed marked alterations on histological structure of lung, which is more than the alteration caused by TiO2-Nps; in addition, recovery period was proved to ameliorate these changes better in TiO2-Nps.