NOVELTY - A 4-methyl-1- pentene (co)polymer composition comprises 4-methyl-1-pentene (co)polymers (A) and 4-methyl-1-pentene copolymer (B1), or (co)polymer (A) and 4-methyl-1-pentene copolymer (B2), or copolymers (A, B1, B2). The (co)polymer (A) has 100-90 mol% structural unit (U1) derived from 4-methyl-1- pentene and 0-10 mol% structural unit (U2) derived from 2-20C ( alpha )-olefin (except 4-methyl-1- pentene). The copolymer (B1) has 99-80 mol% structural unit (U3) derived from 4-methyl-1-pentene and 1-20 mol% structural unit (U4) derived from 2-20C ( alpha )-olefin.    USE - 4-Methyl-1-pentene (co)polymer composition used for forming film e.g. release film and hollow molded articles (all claimed). Uses include but are not limited to film for food packaging, air permeable film, shrink film, easy-peel film, lithium ion battery separator, electrolytic membrane for fuel cell, adhesive material separator, capacitor film, protective film for liquid crystal panel, lens and mobile telephone, bulletproof material, thermal insulation sheet, semiconductor sealing, etc.    ADVANTAGE - The 4-methyl-1-pentene (co)polymer composition has excellent moldability, mold release property, low outgas generation, low staining property with respect to copper foil, and produces molded articles having excellent heat resistance, transparency and dimensional stability.    DETAILED DESCRIPTION - A 4-methyl-1- pentene (co)polymer composition comprises 10-90 pts. wt. 4-methyl-1-pentene (co)polymers (A) and 90-10 pts. wt. 4-methyl-1-pentene copolymer (B1), or 10-90 pts. wt. (co)polymer (A) and 90-10 pts. wt. 4-methyl-1-pentene copolymer (B2), or copolymers (A, B1, B2). The composition contians 100 pts. wt. of copolymers (A, B1). The mix ratio ((B1)/(B2)) is 99/1-1/99. The (co)polymer (A) has 100-90 mol% structural unit (U1) derived from 4-methyl-1-pentene, 0-10 mol% structural unit (U2) derived from 2-20C ( alpha )-olefin (except 4-methyl-1-pentene), intrinsic viscosity ( eta ) of 0.5-5.0 dl/g measured in 135 degrees C decalin, melting point (Tm) measured by differential scanning calorimetry (DSC) of 200-250 degrees C, crystallization temperature (Tc) measured by DSC of 150-225 degrees C and density of 820-850 kg/m3. The copolymer (B1) has 99-80 mol% structural unit (U3) derived from 4-methyl-1-pentene, 1-20 mol% structural unit (U4) derived from 2-20C ( alpha )-olefin (except 4-methyl-1-pentene), intrinsic viscosity ( eta ) of 0.5-5.0 dl/g measured in 135 degrees C decalin, molecular weight distribution (Mw/Mn) measured by gel permeation chromatography (GPC) of 1.0-3.5, density of 825-860 kg/m3, and melting point (Tm) measured by DSC of less than 110-200 degrees C. The sum total of the structural units (U3, U4) is 100 mol%. The copolymer (B2) contains 80-60 mol% structural unit (U5) derived from 4-methyl-1- pentene, 20-40 mol% structural unit (U6) derived from 2-4C ( alpha )-olefin (except 4-methyl-1-pentene), intrinsic viscosity ( eta ) of 0.5-5.0 dl/g measured in 135 degrees C decalin, optionally melting point (Tm) of less than 110 degrees C measured by DSC, molecular weight distribution (Mw/Mn) of 1.0-3.5 and density of 830-860 kg/m3.