ObjectivesThere remain hesitations and miscommunication regarding appropriate public health behaviours and conceptions related to COVID-19. We tested the effectiveness of the community-based health cell approach in improving knowledge, attitude and practice (KAP) related to COVID-19.SettingHouseholds of the Bauniabadh slum area in Mirpur, Dhaka, Bangladesh.ParticipantsHousehold heads (HHs) and homemakers (HMs) of intervention (n=211) and comparison households (n=209).InterventionsBehaviour change communication delivered at the community level in a quasi-experimental manner through small-scale community meetings and home visits.Outcome variables and methodsThe outcomes of interest were before–after mean and per cent changes in KAP scores. Data were collected from HHs and HMs before and after the intervention and difference-in-differences (DID) analysis technique was applied.ResultsWe found statistically significant (p<0.05) before–after differences in the responses to the KAP questions made by the intervention groups. The DID models estimated the improvements in COVID-19-related KAP of HHs by 16.58 (95% CI: 14.05, 19.12), 20.92 (95% CI: 18.17, 23.67) and 28.45 (95% CI: 23.84, 33.07) per cent points, respectively. The DID estimates of KAP in HMs were 17.8 (95% CI: 15.09, 20.51), 22.33 (95% CI: 19.47, 25.19) and 28.06 (95% CI: 23.18, 32.93) per cent points, respectively. Overall, 20.91 (95% CI: 18.87, 22.94) and 21.81 (95% CI: 19.68, 23.94) per cent points of improvement were observed among HHs and HMs, respectively. The DID estimates of before–after mean changes in different KAP domains ranged from 2.24 to 2.68 units and the overall changes in KAP scores among HHs and HMs were 7.11 (95% CI: 6.42, 7.8) and 7.42 (95% CI: 6.69, 8.14) units.ConclusionScientifically valid information disseminated at the community level using the health cell approach could bring positive changes in KAP related to COVID-19.