A polyhydroxyalkanoate copolymer comprises one kind of unit of --[OCH((CH.sub.2).sub.x--SOC.sub.6H.sub.5R)CH.sub.2CO]-- (n=1-7) (1) (wherein R is any one of H, halogen, CN, NO.sub.2, COOR', SO.sub.2R'' (R' is any one of H, Na, K, CH.sub.3 and C.sub.2H.sub.5; R'' is any one of OH, ONa, OK, halogen, OCH.sub.3 and OC.sub.2H.sub.5), CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, (CH.sub.3).sub.2--CH and (CH.sub.3).sub.3--C) and --[OCH((CH.sub.2).sub.x--SO.sub.2C.sub.6H.sub.5R)CH.sub.2CO]-- (n=1-7) (2) (wherein R is any one of H, halogen, CN, NO.sub.2, COO R', SO.sub.2R'' (R' is any one of H, Na, K, CH.sub.3 and C.sub.2H.sub.5; R'' is any one of OH, ONa, OK, halogen, OCH.sub.3 and OC.sub.2H.sub.5), CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, (CH.sub.3).sub.2--CH and (CH.sub.3).sub.3--C) and at least one unit of chemical formulae (3) to (6): --[OCH((CH.sub.2).sub.m--Rz)CH.sub.2CO]-- (n=1-8) (3) (wherein Rz comprises a residue having either a phenyl structure or a thienyl structure), --[OCH((CH.sub.2).sub.k--C.sub.6H.sub.11Ra)CH.sub.2CO]-- (n=1-8) (4) (wherein R.sub.a is any one of H, CN, NO.sub.2, halogen, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, CF.sub.3, C.sub.2F.sub.5 and C.sub.3F.sub.7) --[OCH((CH.sub.2).sub.n--CH.dbd.CH.sub.2)CH.sub.2CO]-- (n=1-8), and (5) --[OCH((CH.sub.2).sub.n--COORb)CH.sub.2CO]-- (n=1-8) (6) (wherein R.sub.b is any one of H, Na and K).