Introduction: Nomophobia has risen in Sri Lanka with increased smartphone use among adolescents after COVID 19. Objectives: Determine the prevalence and associated factors of nomophobia among Grade 10–13 students in post pandemic Sri Lanka. Methods: A Descriptive cross sectional study (January–August 2025) of school children in Colombo, Galle, Jaffna, Anuradhapura and Nuwara Eliya districts was conducted using a self administered questionnaire, including the Mobile Phone Involvement Questionnaire and the Nomophobia Questionnaire (Yildirim & Correia, 2015). Data analyzed with SPSS v25. Results: Of 1,438 participants (61.5% female), all regularly used electronic communication devices. Mobile phones were primary in 96.7%. Other devices: laptops 42.1%, smart-watches 20.8%, tablets 16.8%. Peak use occurred 18:00–24:00 for 58.1%. Nomophobia prevalence (97 .9%): mild 51.1%, moderate 42.3%, severe 4.5%. Across the surveyed districts, nomophobia prevalence was highest in Galle (99.5%) followed by Anuradhapura (99%) and Colombo (98.5%) while lowest in Jaffna (92.9%). Prevalence of severe nomophobia: Nuwara Eliya 7 .6%, Anuradhapura 7 .1%, Colombo 4.6%, Galle 3.8%, Jaffna 2.1%. Higher nomophobia was associated with government schools (p=0.039), Sinhala medium (p