Plastic waste accumulation is still an increasing problem all over the world. In this view, the biodegradation of polythene bag and plastic cup (both in native and in-vitro conditions) by various group of microorganisms isolated from petroleum contaminated soil is investigated. Five bacterial strains, five fungal strains and five Actinomycetes strains were isolated and identified biochemically.  In native conditions, at the end of 6th month, the degradation percentage of plastic was noted as 2.37±0.25% in petroleum contaminated soil and in normal soil as 1.70±0.20% and polythene samples got degraded up to 4.60±0.34% in petroleum contaminated soil and 3.33±0.20% in normal soil. In in-vitro condition, among the five bacterial organisms, Pseudomonas aeruginosa showed highest degradation percentage of both plastic cup (1.34%) and polythene (26.7%). Among the five fungal organisms, Aspergillus niger showed highest degradation percentage of both plastic cup (8.13%) and polythene (32.4%). Among the five Actinomycete sp, Actinomycete sp.1 showed highest degradation percentage of both plastic cup (11.3%) and polythene (34.9%). On comparing to all organisms, Actinomycete strain 1 showed highest degradation percentage. The 16S rRNA gene sequencing revealed it as Streptomyces clavuligerus MTCC 7037. It may be concluded from this work that the petroleum contaminated soil sample is a good source of microbes capable of degrading plastic cup and polythene bag.