Objective To investigate the prevalence of Ascaris lumbricoides infection and contamination of soil with Ascaris eggs in rural areas of Ningxia in order to provide evidence for developing control measures. Methods Total 52 survey sites in 14 counties (cities/districts) in Ningxia were randomly selected based on different geographic and economic situations during 2015-2016. At least 250 residents in each site were enrolled in the investigation. The fecal samples were collected from participants and the eggs of A. lumbricoides in the feces were examined in duplicate under microscope using Kato-Katz method and counted. To investigate the contamination of soil with A. lumbricoides eggs, 10 houses were randomly selected from each site and the soil was collected around their toilets and gardens, the eggs were examined using floating method with saturated sodium nitrate solution. Results A total of 13 850 persons were examined with overall A. lumbricoides infection rate of 2.2% (304/13 850). All infections were light without heavy infected people. People living in Loess Plateau Ecological Zone had higher infection rate of 3.1% （215/6 969） than those living in Longzhong Ecological Zone 1.3%（89/6 881） with statistical significance (P < 0.05). The top three counties with highest infection rates were Pengyang (9.3%, 116/1 250), Haiyuan (2.7%, 34/1 250) and Yanchi (2.6%, 20/760). Ascaris infection in Longde was moderate and the rest 13 counties were low-intensity infection （EPG < 500）. There was no significant difference in the infection rate between male (2.2%, 150/6 886) and female (2.2%, 154/6 964). People with age over 60 had higher infection rate of 3.2% than other age groups. The infection rate of people under 60 years old was increasing with age (P < 0.05). Han people had higher infection rate (2.6%, 214/8 373) than Hui (1.6%, 89/5 434), and infection in housewives (2.8%, 6/215) was higher than other occupations (P < 0.05). People with low education (elementary school) had higher infection rate (2.4%, 125/5 237) than those with higher education, but without statistical significance (P > 0.05). The soil samples were collected from garden and around toilet of 1 068 families and the Ascaris eggs were examined. The highest detection rate was 36.6% （37/101） in Pengyang. The lowest detection rate was 11.3% (9/80） in Yongning with statistical significance between different areas（P < 0.05）. Conclusion There was significant difference in the distribution of roundworm infection in different population such as age, nationality, occupation and education. The soil contamination with Ascaris eggs was common in Ningxia. It is needed to take different approaches to strengthen the control of Ascaris infection in different regions.