Background: Despite having marginal beneficial effects, antibiotics are routinely prescribed in adults with acute sinusitis. Alternative interventions for this common condition are urgently needed. Aim: To assess the feasibility and acceptability of saline nasal irrigation for acute sinusitis. Design & setting: Randomised controlled pilot trial with nested process evaluation in 24 English general practices between October 2019 and May 2021. Method: Participants were randomised to advice to high-volume hypertonic saline nasal irrigation with a delayed antibiotic prescription or usual care. Feasibility outcomes included recruitment and follow-up rates, adherence, and acceptability of the intervention. Results: Of those invited, n = 81/107 (76%) consented and were randomised (42 intervention, 39 usual care). Two participants were excluded owing to ineligibility. Antibiotic prescribing strategies were recorded at baseline for n = 79/79 (100%), with no or delayed antibiotics prescribed in 60% (n = 24/40) of the saline group versus 38% (n = 15/39) of the usual care group. At follow-up, 80% (n = 63/79) of participants recorded whether they consumed antibiotics or not. Among those from the intervention group who returned a symptom diary, 96% (n = 22/23) and 65% (n = 15/23) reported using saline nasal irrigation during the first and second week, respectively. Semi-structured interviews with 16 participants revealed that most were positive about trial participation and viewed saline nasal irrigation as acceptable, noting it as an alternative to antibiotics. Conclusion: Saline nasal irrigation is deemed acceptable for adults with acute sinusitis and a trial of such intervention is feasible. A large trial is warranted to assess the effectiveness of this intervention for this common condition.