The effects of swift heavy ions and gamma radiations upon the nano-scale free volume of the polymethylemethacrylate (PMMA) polymer were investigated using positron annihilation lifetime spectroscopy. The polymer samples were (a) irradiated by 50 MeV Li3+ ion beam to the fluences ranging from 1 x 10(11) to 5 x 10(12) ions/cm(2) and (b) exposed to gamma radiation at various doses ranging from 250 to 1000 kGy. The amorphization was observed in XRD study after ion irradiation and gamma exposure. The absorption edge in the UV-visible study shifted towards the higher wavelength regime leading to decrease of the band gap energy in both cases of irradiations. The formation of new bands at positions 1570, 1560 and 1542 cm(-1) were observed in FTIR study of gamma radiation exposed sample at 750 kGy. The cluster formation was seen in the SEM images. The nano-scale free volume (Vf) of the Li3+ ions irradiated PMMA samples was observed to be decreased at fluences of 1.0 x 10(11), 5.0 x 10(11) and 2.5 x 10(12) ions/cm(2) due to ion induced cross-linking of the polymeric chains. The values of hole radius (R) and V-f were increased at fluence of 5.0 x 10(12) ions/cm(2), it could be due to the clustering induced at higher fluences. The gamma exposures of the samples lead to decrease of the values of R and V-f. (C) 2014 Elsevier B.V. All rights reserved.