The global poliomyelitis eradication programme had a great impact on routine immunization coverage in Lao PDR: DPT3 increased 23% in 1992 to 56% in 1999; OPV3 27% to 64%. However, after the achievement of regional eradication, coverage became stagnant in accordance with the withdrawal of various sources of financial supports. In place of the former funds, a public-private global partnership began to support EPI. We aim to explore factors affecting routine immunization coverage. From February to March of 2005, a cross-sectional questionnaire survey was conducted, targeting 341 mothers living in two districts where immunization coverage was the lowest and the middle in Oudomxay province. DPT3 coverage was 72%, higher than the national target of 65%; however, the drop-out rate was 21%. Influential factors on fully immunized child was distance, literacy, possession of livestock; mothers knowledge of immunization target diseases, measles immunization schedule; and mother's willingness to pay for immunization. In total, 98% of all mothers lived within a 30-minute walk of the immunization site. Household visits increased the immunization status among mothers who were illiterate, utilizing an outreach site for immunization, not willing to pay for immunization, receiving home delivery, and without health education attendance. The much higher routine immunization coverage especially in a district of poor EPI activities suggests a well-designed primary health care approach under the district strategy, the zone-zero social mobilization strategy and good lines of communications; it also points to the benefits of the polio eradication initiative. Household visits were found to be effective for people living with difficulties in such as education, living location, and finance. An equally shared funding system for the basic health as well as international policy for respecting the existing system in poor country is important.