Background: Modified radical mastectomy (MRM) may be associated with severe post-operative pain, leading to chronic pain syndrome. We evaluated whether dexamethasone 0.1ml/kg as an adjuvant to ropivacaine improves analgesic efficacy of Paravertebral block (PVB) in MRM . Method: This double-blind, randomised study was conducted on 60 adult females, scheduled for MRM with axillary dissection. They were allotted into two groups – group R( ropivacaine) (n=30) and group D (ropivacaine + dexamethasone) (n=30) . After inducing general anaesthesia , patients were administered ultrasound-guided thoracic PVB at T4 with 20 ml of 0.2% ropivacaine with and without dexamethasone0.1mg/kg , both as a single level injection. Time to first rescue analgesia, number of rescue analgesia required in 24 hrs and any adverse effects were recorded. Quantitative variables were compared using the unpaired t-test between the two groups. Qualitative variables were compared using the Chi-square test . Results: The duration of analgesia (mean ± Standard deviation [SD]) was significantly longer in the PVB group with dexamethasone (p value- <0.05). Number of rescue analgesic requirement was significantly reduced in dexamethasone group as compare to without dexamethasone.(p value- 0.001) Conculsion:Paravertebral block with ropivacaine and dexamethasone has a longer duration of analgesia than with plain ropivacaine.