Peste des petits ruminants (PPR) is an acute, contagious, fatal disease of domestic and wild small ruminants caused by PPR virus (PPRV). A cross-sectional study was conducted to (i) detect PPRV infection, establish the viral lineage and identify the possible source of its introduction and spread in Morogoro district between November 2014 and January 2015 and (ii) determine presence of PPR in selected villages of Ngorongoro district. Clinical samples of six goats from Morogoro urban and Melela village and 252 caprine and ovine sera from villages within and outside Ngorongoro Conservation Area Authority (NCAA) were subjected to molecular and serological analyses, respectively. Peste des petitsruminants virus was identified in two goats from Morogoro through amplification of the viral nucleoprotein (N) gene. Phylogenetic analysis of the obtained N gene nucleotide sequences clustered the virus into lineage III and was 99% identical to that of Dakawa reported in 2013. Interviews revealed the source of outbreak in Morogoro urban to be introduction of purchased goats from a livestock market in affected district of Mvomero and interaction of herds in a grazing area was a factor for its spread within the municipality. Overall serology results for samples from Ngorongoro showed 58.33% of animals were infected by PPRV. Percentage of seropositive animals (70.54%) from outside NCAA was significantly higher (P=0.0004) than that from within NCAA (48.57%). It is concluded that PPR is not only persistent in previously affected areas, but also is actively spreading to naive areas of Tanzania. It is recommended that veterinary authorities should be vigilant and strict in restricting movement of livestock from affected areas in order to contain PPR.