We present observations of the unusual microlensing event OGLE 2003–BLG–235/MOA 2003–BLG–53 . In this event a short duration ( \sim 7 days ) low amplitude deviation in the light curve due a single lens profile was observed in both the MOA and OGLE survey observations . We find that the observed features of the light curve can only be reproduced using a binary microlensing model with an extreme ( planetary ) mass ratio of 0.0039 ^ { +11 } _ { -07 } for the lensing system . If the lens system comprises a main sequence primary , we infer that the secondary is a planet of about 1.5 Jupiter masses with an orbital radius of \sim 3 AU .