Abstract: The results of investigation on radioactive levels in a total of 28 different rooms in 5 different provinces and cities were reported. The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the wall of the rooms, indoor ²²²Rn concentrations and γ dose rates were measured respectively by Falcon 5000, RAD7 and FHZ672E-10. The results show that the mean activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K in 24 cinder brick rooms are respectively (86±30) Bq/kg, (83±20) Bq/kg, (759±207) Bq/kg, and the mean data in 4 red brick rooms are respectively (51±6) Bq/kg, (54±5) Bq/kg, (632±59) Bq/kg; And in two kinds of wall materials rooms, the mean radon concentrations are respectively (96±42) Bq/m³ and (40±4) Bq/m³, the mean γ dose rates are respectively (133±25) and (120±8) nGy/h. It was confirmed that indoor radiation levels were increasing as a result of comprehensive utilization of coal ash, through analyzing the relationship between indoor concentration of ²²²Rn or γ dose rate and the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K; And preliminarily estimated the annual effective dose to residents caused by the used of wall materials, the range of dose relates to solid cinder brick are 1.6—4.9 mSv/a, and which relates to aerated block or hollow block are 1.8—5.4 mSv/a.

Key words: cinder brick room, activity concentration, ²²²Rn concentration, γ dose rate, effective dose